These are the packages that would be merged, in order:

Calculating dependencies ...

!!! Problem resolving dependencies for =app-backup/backintime-1.5.4
 done!
Dependency resolution took 0.83 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=app-backup/backintime-1.5.4" has unmet requirements.
- app-backup/backintime-1.5.4::gentoo USE="-examples -gui -test" PYTHON_SINGLE_TARGET="-python3_12 -python3_13"

  The following REQUIRED_USE flag constraints are unsatisfied:
    exactly-one-of ( python_single_target_python3_12 python_single_target_python3_13 )