New version 12.3.0 is out https://piwigo.org/forum/viewtopic.php?id=32133
Thanks for the report! I bumped it in tree before I saw this, so can be closed (and 12.3.0 should be in tree on your next sync): https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=f2757ac2b191f5cce7b0e1530399f8962db8783f