Someone please tell me how I am supposed to be on Zoom with my camera on for 3 1/2 hours

There should at least be breaks. Nobody should sit on online meetings for more than an hour at a time without a break if you ask me. Certainly not more than 2 hours without at least a 10 minute break

Have you mentioned about your anxiety? If not it may be worth doing so. They should cater to your mental health needs in this day and age.