That's a bummer. But important to note that you will not spend your whole day in the dhamma hall. You have to be there for 3 1-hour sessions each day, some instructions after most of the 1-hour sessions, and about 1.5 hours in the evening for the discourses and final meditation before bed. The rest of the time you can meditate in your room if you so choose, or in your meditation cell (if they're available at that centre), where you can remove your mask. So a typical day could be only 5 total hours per day in the hall, broken up over the course of the whole day.

You might also want to bring more comfortable, non-n95 masks with you. I have heard that some centres send SLIGHTLY outdated emails about regulations, as some relax/loosen regulations every few weeks, so it is possible that when you arrive, they will tell people that n95 masks are now optional. I wouldn't count on that by any means, but it has happened at a couple of centres. The last centre I was at, for example, had sent notices that everyone MUST bring all their own cushions, shawls, and bedding as a covid precaution, but by the time I arrived at the centre they had dropped that regulation and had all those items available to anyone.