Desktop or mobile?

I’ve recently started using Floorp and I like it a lot. It’s a Firefox fork with more customization options and improved privacy (though not to the level of Librewolf). I don’t remember if it has the button you want to remove since I’ve never used that feature or cared about it.

I use Strawberry for mine.

Are you referring to a drawing tablet? If so, then a good number of ones from the better known brands are supported by the kernel by default. Your safest bet though is Wacom. Wacom is definitely the best supported brand, but it tends to be more expensive than other brands (such as XP-pen and Huion). Non-Wacom branded tablets may require a little bit more initial configuration, like adding a udev rule (I had to do that for my Huion Inspiroy Ink).

The thing you’re looking for is called an Input Method Editor. The only one I’ve ever used on Linux is Fcitx which I really liked. I haven’t used it in a few years though.

This is the homepage for the current version.