Could you bump to v2022.02.14.00 (or some other recent version) if possible? Thanks!
Please also add Python 3.10, drop Python 3.7, and if it works, add DISTUTILS_PEP517_MODE=setuptools.
Sorry, I meant to tag this! It's done. https://gitweb.gentoo.org/repo/gentoo.git/commit/dev-util/watchman?id=b191716697f662cc55a46852733c9ea5edb6b8b0