TempleOS is certainly Intel x86_64, but shy of that there are no guidelines to what machines can run it on the bare metal,
In the FAQ, under "How come it's in the public domain and not GPL?" you can find,
It can run on some bare-metal 64-bit PC's from about 2005-2010 with no layering, libraries, tools, or anything from other sources.
Presumably then there is something about modern x64 bit machines TempleOS can not handle. If so, what are they? What kind of specs does TempleOS require, or what difficulties does it have running on a modern x64 architecture? I know Intel tends to maintain reverse comparability, and I'm not aware of any breaking changes in the architecture.
The README also mentions this, but says it only needs,
- CD/DVD drive
- 512 megs of ram
- Manual I/O port addressing