I tossed mine (in a case) into a tiny, unventilated drawer where it’s happily running Pi Hole and Home Assistant (~15 ZigBee switches, lights and sensors). I don’t think a Pi 4 would thermally enjoy that, plus it’s impossible to get one, so no retirement for my Pi.

edit: it’s a 2 B, the first one wouldn’t be able to run Home Assistant, I think