It's a very good question and I don't know the answer. It was compulsory during lockdowns but "only if you can" which is why loads of staff suddenly developed hidden disabilities to get out of wearing one. The worst perpetrators were the checkout staff and supervisors, which as a customer would...
I have not stopped wearing mine whilst working in Tesco. I am sadly only 1 of about 5 members of staff who are though, which is very poor. Those who were wearing hidden disability lanyards in order to not wear a mask during lockdown etc have stopped wearing those too, which is pissing me right...