

I think Nobara is the other most(?) popular choice by gamers.
I don’t have much experience with gaming distros. I just think whatever it is, a computer shouldn’t bee too locked down for a kid so they can also install other things, try other tools like an office suite, video editing or content creator stuff and maybe even have the experience of messing up. Within limits of course.
I’d go with the Full Disk Encryption. You can be sure everything is encrypted that way. Any additional complexity adds ways to mess up and compromise security. Entering the password is a bit cumbersome. But that’s part of the deal. I just carry my computer keyboard to my NAS and enter the password each time I need to reboot. Which doesn’t happen that often. There also used to be some tutorial somewhere on how to put a Dropbear SSH server into the initrd so you can enter the password over network.