Please rekeyword dev-python/PyQt5-5.15.5 (or later) which introduced a new dependency on dev-python/PyQt-builder. Thanks.
Unable to check for sanity: > no match for package: dev-python/PyQt5-5.15.5
Looks like this was done in commit ae5e836e1497ebd62a80a3e38f63b530ccfb1395 but the bug wasn't referenced.