Now that apple has their own silicon, all the older intel based MacBooks are pretty cheap. I just replaced my wife’s 2013 MacBook Airs battery, upgraded the drive, and installed Linux. It’s been a solid little laptop. Not the fastest but there’s probably a few pro models within your price range. Just make sure to get at least a 16gb model since the ram is soldered. Might have issues with the webcam, but the wifi drivers are pretty good.
This should add the flathub remote to the system and then install all the existing user packages into the system level. Then removes all the user level packages.
flatpak --system remote-add --if-not-exists flathub https://flathub.org/repo/flathub.flatpakrepo flatpak --system install $(flatpak list --columns=application) flatpak --user remove $(flatpak list --columns=application)
Personally I would just pick all the ones you’d like to be global (system level) and leave the rest at the user level.