/lib/udev/rules.d/64-btrfs.rules contains a line
@rootbindir@ should be replaced with a file path.
eudev-3.2.6 has the same issue on void linux, too.
Should be fixed in the latest package. (https://gitea.artixlinux.org/packages/eudev/commit/14cfa861047f6f4e31f6309a945094cd99de8192)