Yes they do last a long time. They can be a great option. Just not easy to fix if something goes wrong.
You don't have to clean a regular chain that often, but it will last longer if you do. A regular chain is perfectly fine to use in the rain / snow/ etc.
In my mind, I know the chain and cassettes will wear out, so when they do, I would rather have ones I can replace myself. But an internal geared hub is a great option as well. It is lower maintenance, but with the trade off that it is difficult to work on.
Ah, gotcha.
I'm not technical enough to understand the functional difference between flatpak and snap, but I know that snaps are centrally controlled by Canonical and thus I assume not as enshittification resistant as flatpak.
But from the end user perspective, they can be a lot simpler to use than PPAs for random software. For me they're kind of a guilty pleasure.