The goal is to be distro-agnostic, but I find that Flatpak and Snap both add more bloat than is worth it. Either just use distro packages, or, if you really want cross-platform, get an AppImage and be done with it.
While that's in theory, reality is much more harsh. Treble implementations vary greatly between OEMs. For example, Samsung phones don't have mobile data working because of proprietary RIL used by Samsung. Also, Treble compatibility often breaks on newer versions of Android, especially for Pixels (which is quite ironic). Treble is really meant to make the job easier for OEMs and ROM devs to continue supporting a device. The GSI is really meant as a way to certify Treble.
I really like the idea of Étoilé, but a lot of the docs are outdated because of the death of Gna!, and right now the focus is more on the CoreObject framework rather than the UI.
Plus, both Corellium and Asahi Linux are porting Linux to the M1 MacBooks. I have Ubuntu installed in a separate partition and boot into it occasionally. The main issues right now are audio and graphics support.
Exactly why I prefer Seaglass over Element for Matrix chat, even though Seaglass hasn't been updated in a while. Same with Telegram Desktop and Telegram for macOS.
Then there's Android One, but that is an absolute disaster at this point, with unoptimized software and updates that brick phones. Google themselves haven't been doing too good on software reliability this year; just look at Android 11, especially on the Pixel 2 and 4a. Both have huge bugs and in the 2's case, they will never be fixed. And some Android 11 bugs won't be fixed until Android 12 comes out.
I'm seriously considering a switch to iOS at this point.
Telegram is surprisingly good. My entry point to the Telegram rabbit hole was the Android development community, and I've found quite a few people who are willing to discuss stuff. We also have a lot of fun.