I think it's absolutely to resign rather than work in a place where you feel your health is in danger. I'm not sure where you live, but where I live that place would get shut down if someone reported staff not wearing masks.

It doesn't really matter about anything else but how you feel. If YOU feel unsafe, then it's perfectly reasonable to do whatever you need to do to remedy that. If that means resigning, then resign. It's an employee market right now. Employers are struggling to hire people (in general, there are certainly fields where it's harder or for upper management, etc. might be harder).

I don't know if you read my thread in the Poobah subforum, but I walked away from a huge contract this week because of my mental health. Your physical health is just as important. If it were me, and I feel the same as you about masks, I would have left my first shift seeing employees not wearing masks and not come back.