id's Doom (and Quake) level editors were written for NeXTStep which ran on NeXT hardware which was based on the Motorola 68030 or 68040. OpenStep later made it to x86 (also PA-RISC, SPARC, and via OS X, PPC, x64, and ARM64) but the level editors used the original NeXT classes (NX* instead of NS*) which didn't make the transition to OpenStep.

https://github.com/TCRF/old-doom-stuff

https://github.com/FreeSlave/Quake-Tools/tree/master/QuakeEd

Practically all id's revenue came from DOS games in Doom era. 99%+.

I played Doom at work--I got a PC to run OS/2 and C compilers.