I don’t use Flatpaks much but having read many posts about Linux stuff it seems possible your issue is permissions. IIRC you can use Flatseal to fix that.

Not sure how much help it’ll be to you but often the best place for technical info is the Arch Wiki. Good luck!

You can install newer kernels from the update manager in the system tray. Then it’s View > Linux Kernels iirc.

Your issue is possibly something to do with configuration of Pulse Audio / PipeWire. Probably the best place to ask would be on the Linux Mint Forums.

Break free from Google! By buying a Google phone…

and Mint also contains proprietary elements

Good luck finding a distro that doesn’t https://www.gnu.org/distros/common-distros.en.html

I advise to not let perfect be the enemy of good and to start with Mint. It’s where I started and now I also use Arch and Debian on other machines.