Earlier quoted context omitted.
>which means listings won't work on real hardware. They will. LEG is a subset of ARM. What won't work is ARM software on LEG hardware. I would recommend getting the current edition, which has replaced ARM/LEG with the industry standard RISC-V.
Does RISC-V version include GPU? I am more inclined for ARM version since that's applicable to both all current Apple hardware and school Chromebooks.
The ISA doesn't really matter (at least, not between MIPS, ARMv8, and RISC-V) when you're first diving into computer organisation. That's why one book can be sold with three different ISAs. The overarching concepts are mostly the same: you have digital logic, IEEE-754, basic assembly (add, sub, and, not, xor, load, store, shift), pipelining and hazards, caches.
Only afterwards do the differences between the ISAs come to play, when you have complex vector and ISA-specific instructions, superscalar pipelines, atomic instructions, etc.