All, I was able to resolve this by dropping `--with=kf6` from debian/rules. The mistake I made was not using a package that had already moved to Qt6/KF6 as a reference point. Looking at kcalc 24.08.0's packaging resolved the mystery.
Thanks for all the help, everyone! I'll be back with an ITP soon-ish. Best, Antonio
OpenPGP_0x72DB026E04C1C768.asc
Description: OpenPGP public key
OpenPGP_signature.asc
Description: OpenPGP digital signature