When I first started using Linux 15 years ago (Ubuntu) , if there was some software you wanted that wasn’t in the distro’s repos you can probably bet that there was a PPA you could add to your system in order to get it.
Seems that nowadays this is basically dead. Some people provide appimage, snap or flatpak but these don’t integrate well into the system at all and don’t integrate with the system updater.
I use Spek for audio analysis and yesterday it told me I didn’t have permission to read a file, I a directory that I owned, that I definitely have permission to read. Took me ages to realise it was because Spek was a snap.
I get that these new package formats provide all the dependencies an app needs, but PPAs felt more centralised and integrated in terms of system updates and the system itself. Have they just fallen out of favour?
It really depends on what you are using them for. I would avoid Snap as it is a mess but flatpaks are fairly similar to regular apps. The big difference is that the app configs are in home/var/local and Flatpaks use sandboxing.