You can install/remove/update flatpaks via gnome software. Gnome(and a bunch of other DEs/WMs) provide an integrated version of xdg-desktop-portal.
Other than that, flatpaks work everywhere. Even on gnome.
Be really careful with flatpak “sandboxing” The applications themselves define how much sandboxing is applied. Many of them have wide access to system resources. This is made worse by the fact that flatpak controls aren’t very granular so you often have to give flatpaks access to more of the system than they really need.
flatseal is a simple GUI tool that lets you review and modify a flatpaks permissions.
Sometimes the flatpak version of an app works differently than the Arch Linux repo version.
Case in point. I store all my music and videos on my enos Server, and use minidlna to stream them.
On the client side, I use VLC as my DLNA client. I have 1014 mp3 and that is too many for the Arch repo VLC to handle. On the other hand, the flatpak version of VLC handles that many items perfectly as expected right out of the box.
Also if one changes fonts, themes, icon themes, etc all the time, the Flatpak version’s theme is what videolan (the entity that develops VLC) sets it to. With VLC flatpak it is pretty much adwaita and light or dark.
Nope, and as easy as the fix is, and as lazy as I am, I haven’t bothered looking into it.
I use KDE Plasma which EnOS installs vlc as default. So I simply remove the Arch repo version, and install the flatapak version. Easy, peasy.