After updating QT libraries from 5.15.12 to 5.15.13 hydrus for whatever reason was loading QT from dev-qt/qtstyleplugins and failing with error `Cannot mix incompatible Qt library (5.15.12) with this library (5.15.13)`. After rebuilding dev-qt/qtstyleplugins problem was solved
Your world update is likely incomplete (maybe got a build failure or so), this package already has a binding operator and would be scheduled for a rebuild.