American here. I don’t really go anywhere anymore, but ducking into a McDonalds, Home Depot, or any major chain has always been an easy bathroom option. I don’t think this has changed, unless drastic changes have happened in some major cities. I’m not in those cities.
The only change I've noticed more recently is more places that you described (especially fast food) has started to add door codes. Easy enough to ask an employee for the code though.
One data point, but the building housing bathrooms in the local park has been closed for renovations for a very, very long time. Now there are two porta potties instead. They stink like hell but I do see them get pumped out by a truck occasionally.
I don't know if the renovation delay is classic lowest bidder contractor failure, grift, by design, or some combination. Anyway, no running water for people sleeping outside in my neighborhood.