For understanding what's going on all the way down to the ISA level, I'd say something like a PIC microcontroller is even easier since they tend to have only ar

For understanding what's going on all the way down to the ISA level, I'd say something like a PIC microcontroller is even easier since they tend to have only around 50 instructions, though RISC-V has the advantage that it could scale all the way up to potentially desktop CPUs some day