I've been searching for options to emulate x64 OSs over Apple Silicon, and it seems that every solution I find is based on QEMU. Is it really the only codebase that can do this at present? (July 2022)
There are many alternatives to QEMU that can run other OS sharing the same architecture (Fusion, Parallels, Virtual Box, etc).
QEMU also does dynamic binary translation for a virtual system. This allows booting an entire operating system. Rosetta and Microsoft Windows x64 emulator can translate applications on the fly (dynamically).
If you are looking to boot Linux, FreeBSD, or other x86 operating systems on the M1, the options are currently only QEMU. UTM is a GUI package of QEMU natively built for MacOS.
All solutions are based on QEMU because it is the oldest and most mature code for this task. The original version 0.10.0 was released in 2009.