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

Calculating dependencies ...

!!! Problem resolving dependencies for =x11-misc/bumblebee-3.2.1_p20210112-r4
 done!
Dependency resolution took 0.83 s (backtrack: 0/20).


!!! The ebuild selected to satisfy "=x11-misc/bumblebee-3.2.1_p20210112-r4" has unmet requirements.
- x11-misc/bumblebee-3.2.1_p20210112-r4::gentoo USE="bbswitch" VIDEO_CARDS="-nouveau -nvidia"

  The following REQUIRED_USE flag constraints are unsatisfied:
    any-of ( video_cards_nouveau video_cards_nvidia )