[Arnavion]

Turing Complete - https://store.steampowered.com/app/1444480/Turing_Complete/

I also made my own assembler as part of learning the ISA and put it at https://github.com/Arnavion/riscv . You can see a screenshot and video of the CPU in action there.

The game's campaign walks you through creating a simple 8-bit CPU and then a larger CPU similar to old ARM. But then it also has a sandbox to do whatever, and you can use whatever design you want to solve the puzzles intended for the original two CPUs.