That's like saying you can use email if you like living in the 70s-80s. XMPP is a pretty healthy and active project that is standardized like email and ActivityPub. I would consider XMPP pretty modern, especially considering its features, extensions, etc., as well as the numerous applications it is integrated in.
XMPP is also used in very popular games, consoles, and clients.
XMPP it is, then.
Windows: What is my purpose?
User: You are a bootloader to install Linux.
I would probably suggest Mint. When I first started Linux, I was adept with computers, but I still struggled using Linux for the first time. I tried Fedora around 2015 as my first distro, and I really struggled to install it. So I started with Ubuntu. I spent time doing some courses for Linux, and it was quite a journey for me to figure out this new environment. Then I would distro hop so much because I was dissatisfied with missing packages and issues with my new laptop (which wasn't running well on many distributions because it required a newer kernel), and then I landed on Kubuntu for a little while. Then Manjaro, which I don't recommend anymore for these reasons (plus I had to reinstall Manjaro a few times when it broke, especially due to NVIDIA driver issues, but today that shouldn't be as much of a problem, I believe). I was able to install Manjaro with Manjaro Architect at one point, which made it easier for me to figure out how to install Arch Linux. I was breaking my Linux machine so much when I was using Ubuntu because I didn't understand what I was doing, thus it is difficult for me to recommend a Linux distro to a new user with full 100% certainty they would not break their system if they wanted to do some tinkering or try to do any niche thing like gaming. I know you want to leave Windows ASAP, but it may be easier to first run Linux in a virtual machine. It's going to take a while to figure it out, and a virtual machine will help make the journey less painful so you don't risk wiping your drive or having periods where you are stuck without a machine when you need to get work done and you are sitting in front of your computer for hours trying to install and configure Linux or figure out why you are booting into emergency mode. For a tip, I really recommend not installing everything you want under the sun. This was the reason for 90% of the time I broke my Linux installations. Install only a few packages at a time, and backup your data.
There is a new Arch-based distro in town that is meant to be user friendly, which is Crystal Linux, but I haven't used it myself nor do I know if this is good to recommend to absolutely new users. The reason why I mention it is because I have had a lot of trouble with other distributions, and while Arch would break on me once in a while (which at that point in my Linux journey, I could fix Arch without needing to reinstall the entire OS)--usually for a specific package or two--as a noobish user it was a better experience for me working with the pacman package manager and having access to the Arch User Repository. I also had a better time working with rolling release distributions. With Crystal Linux, it gives you the option to install the Nix package manager and comes with a nice pacman wrapper called Amethyst, but I would consider yay the best pacman/AUR wrapper, imo. I haven't tried Amethyst, though.
Here's a video on Crystal Linux by DistroTube: https://yewtu.be/watch?v=Q_CXNtbsy74
Crystal Linux also has documentation on using a NVIDIA GPU with Wayland here: https://getcryst.al/site/docs/crystal-linux/nvidiawayland
Crystal Linux also uses the BTRFS filesystem utilizing snapshots with Timeshift, which if I had used this when I was first learning Linux, it would have saved me a lot of trouble.
Also, one last tip: when installing Linux or working with something you are unfamiliar with, take notes. It really helps to have something to look back at when you have to do the same task again and forgot the reason you did certain things.
I have done so (git clone) with Gentoo and it works.
I know developers are busy, and I don't mean to berate them for their choices or work. I only have a two year Computer Information Systems degree and haven't programmed a lot for a while, but supporting the XDG specification and remaining backwards compatible doesn't seem to be very difficult or would cause so much breakage (of course, the amount of work would depend on the software and how the hardcoded path is implemented). I look up git repository issues for the software and tend to find ubiquitous examples like vim to be resistant to such change: https://github.com/vim/vim/issues/2034
This is really frustrating and leads me to find alternative software, such as neovim/doom emacs instead of vim, nushell instead of bash, etc., just to be able to clear up my home directory. I don't mind if I have to wait for XDG to be supported, but many important projects just label the issue as "won't fix". I totally understand where you are coming from.
List of software with hardcoded paths at this time: https://wiki.archlinux.org/title/XDG_Base_Directory#Hardcoded
This is not an Android phone, but I plan to get a PinePhone Pro and then maybe a flip phone for calls. I want to be able to tinker with Linux on my phone and have better access to Linux applications and utilities. It's not the most secure option, but for me, I don't need much from a phone, though it would be nice to have more freedom and capabilities with my device. Plus the physical keyboard accessory looks super nice. This may or may not help you, but I figured to share my thoughts just in case. I don't know how knowledgeable you are with Linux, but you will need to be an intermediate Linux user (or willing and able to dedicate the time and effort to learn) and be willing to accept the limitations of the device, especially since it is not really meant for normal users yet. It's meant for people that like to tinker and can contribute improvements and testing for the device. PINE64 makes a lot of cool tech, including the PineTime, Pinecil, PineNote, etc., and they are very focused on repairability as they sell individual parts for each of their devices and provide long-term support: https://www.pine64.org/
I have had a OnePlus 6T that I have installed LineageOS on and have replaced the battery even though it is "non-removable".
Battery Replacement Prerequisites/Tips
You need a heat gun to heat the adhesive to open the phone case. Then you need some spludgers/opening picks and a suction cup to open the case, as well as a precision screwdriver kit (essentially, get an iFixit kit for the opening tools). You will need some adhesive tape or some B-7000 or T-8000 to reattach the back cover. Be careful with the back cover as it is made of glass; I cracked mine by bending it too much and still have to get around to replacing it with the transparent cover I bought (which will look ugly with the replacement battery, but I figured it would be very functional as it will help me keep an eye on the battery before it expands too much and breaks the phone like my previous LG G5).
I recommend this video to follow along for the battery replacement: https://yewtu.be/watch?v=KDJJ9FOQEXk
I have had this phone for about 4-5 years now. If I need Android for any reason, I plan to use this device for those purposes.
I also use a Unicorn Beetle belt holster case with the OnePlus 6T, and it's survived so many falls because of it. It's only around $10-20 on eBay (try getting an Otter for that price). You can still find a 256 GB model of the phone for less than $200 on eBay as well. I recommend any OnePlus phone up to the OnePlus 7T Pro. Their newer devices now have an encrypted battery, and the company itself sucks, but their older phones are good for rooting and custom ROMs and are pretty high powered and inexpensive for their flagship models, which is why I picked them when I was looking for a phone.
Then again, after learning about the crappy things the Raspberry Pi Foundation has done, I'm probably better off getting a used Lenovo ThinkCentre or HP EliteDesk Mini (which I already have) for a much lower cost. I was just excited about Raspberry Pi's finally being powerful enough to handle 4K, but that may be a stretch, too.
That seems to work for my needs. The performance improvements according to this video seems promising: https://yewtu.be/watch?v=9hYfQ7bRgZg
Finally, a pi good for 4K video! (Apparently Raspberry Pi 4 could as well, but I am assuming this is an improvement. I still have a couple of Raspberry Pi 3's.)
I will be honest, I haven't came around to using XMPP myself yet, but I am pretty sure you are able to do all of those things, at least with the help of extensions. Here's the XMPP standards that are currently stable or experimental:
Files/Images:
Emojis/Stickers:
Looking at clients, I see various ones that have at least some of the features you are looking for (especially file and image sharing, I haven't found a client that has explicitly implemented the stickers specification yet, but Movim seems to have them):
I would give it some more time. It seems those features are in development, but this is essentially an alternative to Matrix that is more standardized. It's a widely adopted and integrated protocol, so I don't doubt the features you are looking for will become more fleshed out some day.