Gentoo's Bugzilla –
Attachment 685416 Details for
Bug 768204games-puzzle/brainparty-0.61-r1 with gcc-11: /usr/lib/gcc/x86_64-pc-linux-gnu/11.0.0/include/g++-v11/bits/stl_tree.h:785:15: error: static assertion failed: comparison object must be invocable as const