User Repos
system packages, AppImages, and Flatpaks cover almost everything that the average user could need but sometimes you need something that either doesn't work as well in its official version or you need something so specific that only other users with your issue would care to make it.
For this we have user repos, user repos are databases of packages made by a distro's user base to fill gaps that aren't already met by alternatives. The most notable example being the AUR or the Arch User Repository. The AUR has tens of thousands of packages and is famous for the wide range of software that it offers. In many ways it's the primary selling point of Arch but this system exists on other distros too. Fedora offers Fedora COPR and Nix offers Flakes. They aren't as vast but they are solid and may be necessary if you really can't find something somewhere else.
Disclaimer: user repos are not inherently safe and user made packages sometimes may and have at times contained malware. It goes without saying but if you wouldn't install a sketchy Github project or torrent something without checking the same should go for the AUR or any other platform like it.