Fork of android firefox
It is possible and for backup use timeshift
Maybe try arch based distro like garuda and endeavouros since those would be the most easiest to fix if any problems.
Well there is lightly-qt which changes the buttons for a more rounded theme.
What are you running it on ? Specs
By stability issues you mean does it crash or too updated.
Well understandable , since thats the default look. But KDE is one of the most customizable DE, you could make it look like anything you want.
You could use pavucontrol,since discord mainly uses pulseaudio controls
Before asking maybe check the archwiki since most problems usually have solution there.
You can change the kernel if you want through update manager.Linux mint doesnt always follow with ubuntu.
In mint have you tried the latest kernel through update manager ?
Its is pretty solid choice for arch users . It is like what mx linux is like to debian.Its good for beginner to try out arch though when you are using arch you kind of have to be always ready if something goes wrong.