It is straightforward to run an x86 macOS VM on Linux with QEMU & KVM. It's against the EULA to do so on non-Mac hardware, but technically it is possible.
"Virtual Hackintosh" is definitely quite popular, especially in regions where EULAs are not enforceable. But no one has managed to emulate the M1 enough to run the full OS yet[1], so that's a strictly x86-only option.
[1] I believe this is the closest publicly documented effort, and it's a year old: https://news.ycombinator.com/item?id=25064593