We recently discussed what builders do already work with CP. Sharing here in case it is useful to you:
"We do have Beaver Builder publicly supporting CP.
FX Builder was developed for CP by forking a plugin for WP and I have it on some of my sites because it’s just GREAT.
Thing to note BB and FX are not compatible with one another but that is not a problem since one of the two is usually enough to develop a site."