100% CPU use doesnt make sense. RAM would be the main constraint not the CPU. Worth looking into - maybe a bug or broken piece of software.
Also the DE may he more the issue than the distro itself. You could install an even more lightweight desktop environment like Open box. Also worth checking whether youre using x11 or Wayland. Its easy to imagine Wayland has not been optimised or extensively tested on something like your device, and could. Easily be a random bug if the DE is pushing your CPU to 100%
There are super lightweight distros like Puppy linux.


















Any points and click adventure game, there are loads including old classics and modern good games.
Monkey Island remasters are fun and can be played with mouse. Broken Sword games are also good.
Rusty Lake games are great if you prefer more puzzle games than narrative ones. Still has a great somewhat surreal plot just not like a point and click narrative game.
Also If you havent played dwarf fortress now is the time to learn, the siege update came out this week. Mouse or keyboard, or both, but definitely can be done one handed.
Vampire Survivor that others have suggested is a good shout, one hand on the keyboard is enough and its very addictive.