“Covert” does have multiple definitions, after all, and the Mandalorian in green looks more feminine to me than the others in armor.
I’m not saying this person is Sabine Wren (despite the actress’ willingness to play the character in live-action) or Bo-Katan, but they could be significant!
“Covert Mandalorian” may simply be one of the many nameless Mandalorians who were in the covert on Navarro before they were wiped out after helping Mando and Baby Yoda escape, but “covert” could also mean that there’s more to this Mandalorian than meets the eye.