I had troubles with the Ubuntu Software App (20.04/22.04), it simply wasn't starting.
I found out that although the app is still advertised as Ubuntu-Software it is actually a snap called snap-store.
And that is a mess, in the Activities you have to search for ubuntu-software and CLI for snap-store.
As it seems Ubuntu is moving more and more to snaps, I thought Ubuntu-software was renamed version of gnome-software, but not anymore as it seems.
Anyhow, I succeeded in updating Ubuntu-Software/snap-store (killing it first to be able to do snap refresh snap-store), but I can't find any references to Flatpak installs in the snap store.
How do I get support for Flatpak in the snap-store?
Best Answer
"Ubuntu Software" does not support flatpak.
If you wish flatpak support in the software center, you could install Gnome Software instead:
This installs both flatpak and snap support in Gnome Software.
You can optionally remove Ubuntu Software with
sudo snap remove snap-store.