The NeXT variant did run on the following architectures:

1. Motorola 68k (the original NeXT hardware had 68030 and 68040 chips)

2. Intel x86 (NeXTSTEP 3.1 for Intel was released in 1993)

3. HP PA-RISC (I have an OPENSTEP 4.2 CD that can run on Motorola 68k, x86, PA-RISC, and SPARC hardware)

4. Sun SPARC

5. 32-bit PowerPC (Rhapsody, the original Mac OS X 1.0 that was essentially still Rhapsody, and of course Mac OS X from Cheetah through Leopard)

6. 64-bit PowerPC (Power Mac G5 and iMac G5)

7. Intel x86-64 (starting from Mac OS X Tiger all the way to macOS Tahoe)

8. 32-bit ARM (iOS on early iPhones with 32-bit ARM chips)

9. 64-bit ARM

I could be forgetting other platforms, but these are the ones I know from the top of my head.