It's hard to deal with a parent who doesn't respect your boundaries. I agree, I don't think more transistors can adequately solve what is actually a communication issue. I hope OP looks into codependency/enmeshment, because some parent-child relationships, especially mother-son ones, become enmeshed, and this results in things like the mother not having appropriate boundaries with the son. This might look like, for example, frequently interrupting you in a private space.
Maybe the reasons he doesn’t get into is that the only working toilet is only accessible through this room and his mom cannot avoid going in several times a day. Maybe it also stores her Polly Pocket collection and she has a strong need to check a specific doll multiple times a day. Knowing moms I consider the later more likely