I always figured that enbies just used whatever bathroom is more convenient, gender neutral bathroom are usually pretty uncommon so it must be very difficult.
Train stations and shopping centers frequently have accessible (for the disabled) or family restrooms, which are generally non-gendered, but at Tokyo Big Sight in particular, there are only men's and women's bathrooms. And despite the cleaning staff for bathrooms being whatever gender is available, the bathrooms themselves are
very gendered. I totally get wanting to find a porta potty or something else that doesn't involve having to deal with crowds. Japan can be an extremely frustrating place to be nonbinary or agender.