Lemmy is actually interesting as there could be four implementations (or five if you consider none).
- Standard instant push notifications (you get them in app and out of app)
- Push notifications only while app is open in forground (example lemmy web ui only has notifications when tab is open)
- Polled notifications (notifications that occur after preset interval).
- A combination of the above three (ex: polled notifications in background push in forground)
- No notifcations at all
Just some thoughts
In the case of this instance (lemmy.fmhy.ml) it appears to be self funded by the admins
https://www.reddit.com/r/FREEMEDIAHECKYEAH/comments/xrxen7/faq_support_thread/
However currently for others instances donations seem to be the primary method of funding (beehaw has a nice cost breakdown)
Edit FMHY link to beehaw post:
https://lemmy.fmhy.ml/post/509214
Beehaw direct link to post
https://beehaw.org/post/920683
https://beehaw.org/post/428209