Those apples are oranges
Intel and AMD both share the same instruction set (although support for extensions may differ between processors) - RISC-V and Arm are two different instruction sets.
RISC-V defines an ISA + allows you to add your own instructions. Some open-source HW designs are available.
Arm defines an ISA + allows you to add your own instructions on M-class processors. You can design your own core if you have an architecture license or license one of Arm's own designs (which is what most companies do).