In order for him to go in by himself in a wheelchair, there needs to be a push open door button on both sides. Once in, there needs to be room to go in and turn towards the toilet and have a grab bar next to the toilet. Honestly, if we are in the truck or just parked, he uses a urinal we keep in the truck. No other option. He can't stand for long at all, maybe a minute, and transferring a 275lb man is very challenging. Ask me how I know. So, yes, I've been in the men's room many times. If it's not single use, I open the door and yell if anyone is in there first. If so, then I just wait. Our home bathroom is designed very well for him. We had it put in when we moved here, and a huge bedroom on the ground floor. I can help him in the shower, dressing afterwards, and at the toilet. We have a chair that he can transfer to at the sink (a pedestal sink) to do his other stuff, and a medicine cabinet with his stuff in there that he can reach sitting down. And a shelf on either side of the sink with more stuff he has that he needs.
Anyway, we do figure it out, just takes time. The stupidest thing was our ADA required staff bathroom at our preschool when we were designing it. It had to have a handicapped shower with a seat, a roll up shower. Why? I don't know. And it was expensive. No one needed to come to work and shower, that would be very weird. And we would not shower a student.