I heard that in 1.16 pillagers can pick up and wear illager banners. So in 1.16, I went to a pillager outpost in creative and killed the captain. It dropped the banner alright but other pillagers didn't pick up the banner. I did the same thing to a patrol that was nearby and killed the captain, but none of the villagers picked up the banner to wear on their head. Last I went in my creative invotory and got a villager banner and dropped it and the pillagers picked it up and wore it on their head. So basically pillagers won't pick up villager banners that spawn naturally(outpost, outpost captains, patrol captains)but will pick up illager banners that players drop in the creative inventory.