I self hosted matrix for probably a year after me and some people started getting spam on telegram. It was the first thing I really self hosted beyond jellyfin (and plex before that) so I didn't really fully understand what was I doing and that could have affected things.
I had a few hurdles that made it not work out for me and my friends/family. First, the end to end encryption, one of the main "selling" points I feel, makes it complicated to sign in for people who don't care about any of that. You end up getting a code to save, I had to verify them at first, we'd have times where something still showed unverified, etc.
Just started hosting nextcloud recently and I'm also seeing the notification issue, but at least you just sign up and start using it.
I also noticed in matrix we never got notifications for emoji reactions (which we all use with each other). Other notifications were relatively solid though.
I never got webrtc and some stuff working and I sort of lost steam trying, so we could use element or fluffychat but not element X and we couldn't have big group calls or anything like that. That's probably on me though, but in fairness nextcloud aio just has a checkbox and all that stuff works.
Since I'm the only dork in my little group interested in this stuff I abandoned matrix when nobody used it.
It's a brand.