Backgrounds Granting Feats

I am trying to figure out the custom builder to add on the things I am missing as they come up for my characters, because the character sheet app is otherwise great.

For the sake of this, consider the Rewarded background, which grants you the choice of Lucky, Magic Initiate, or Skilled feat. If you take a feat, it should then make taking it again later inpossible, but for the life of me, I cannot figure out how the system is flagging that each character already has a feat or not.

It is technically possible to include via the "select feat" effect, but that also allows selections that arent a part of the background.

Has anyone made an actual tutorial for this thing yet?