Debian is a free operating system (OS) for your computer. An operating system is the set of basic programs and utilities that make your computer run. Debian provides more than a pure OS: it comes with over 59000 packages, precompiled software bundled up in a nice format for easy installation on your machine.
display graphics drivers comes baked into the kernel, you don't need to install anything, they are already there. messing with them is a bad time if you don't yet know what you are doing.
first things first take a look at your system logs to see what went wrong. depending on your installed vpn you should be able to just apt purge it.
As far as reinstalling and losing your data, you may want to just backup /home to a USB disk now.
You'll want to figure out the VPN issue, so maybe post what you know about that. Also post ifconfig -a or ip addr show. Also the output of route for good measure. Can you ping anything? Is it just a nameserver issue (try pinging 8.8.8.8 and kernel.org, for instance)?
Once you have network access, I'd install tmux if you're going to be spending any significant time debugging in the terminal :)
Also post ifconfig -a or ip addr show.
ifconfig is deprecated for a long time I think. Not even sure if some Debian package still provides it. I've switched to ip a and ip r and cat /etc/resolv.conf to look at such issues as OP has.
You should be able to use nmtui tool in the text terminal to activate your network connection. From the terminal you can also use the startx command to try and see if that would show you a GUI or other useful errors.
If secureboot is enabled try disabling it. If disabling secureboot resolves the issue re-enable secureboot and add the dkms signing key with mokutil: https://wiki.debian.org/SecureBoot#Making_DKMS_modules_signing_by_DKMS_signing_key_usable_with_the_secure_boot
This has nothing to do with secureboot, as the system boots fine according to the explanation.
That doesn't mean it is loading dynamic kernel modules, which also require enrolling a machine owner key.
the apt logs probably contain the versions you had before that. you could try and go back.
in any case: make backups before updates to prevent this in the future. even an incomplete backup can be better than none.