Went to a supplier visit earlier in the week, and it's the first time in a year I've had to sign a covid predeclaration and come armed with a negative test (I actually forgot, but they had tests at their reception). They also supplied masks for people who hadn't been vaccinated. The reason is that they have some clinically vulnerable people working there - and of course want to protect them.
The way they handled it was subtle, and seamless. One of the people there (not a colleague) didn't want to tell them of their vaccination status, which I didn't understand - so he had to wear a mask to come in.
The way I see it, you're visiting someone else's domain, you follow their rules. Just like I expect people to take their shoes off when visiting my house. You follow the requests of your hosts. Even if you disagree with it, is it such a hassle?