Group physicals at work seems unusual, but I had once a group X-ray of the lungs in the 1980's. I don’t remember if it was mandatory or not. We had to remove our shirt.
I'll concede it would be very uncommon, but I also never had them at school so that concept is equally alien to me even if it does happen in reality. I went to private school growing up so they never even offered such a thing; it was just assumed the families paying tuition had their private doctors and jobs that allowed time off to take the kids they'd go to so there was no incentive to provide an alternative.
At the same time, even with the PTO offerings my job has, getting to the doctor for routine exams is inconvenient as hell. I don't have a car and public transit sucks, so I pretty much have to take half a day for a fifteen minute appointment because of bus transfers and walking time. If they brought in a physician, dentist, and optometrist and offered the exams without having to use sick time or find a location that takes our insurance, I'd jump on it even if it meant stripping down in front of my colleagues (presumably such an exam would be divided by sex no matter what, whether it's two separate locations or just different time slots, although an adequate incentive could make that not matter to me either).
I think I would pass as there seems to be little incentive to attend a group physical at work.
I could there being incentives to be offered. My job's insurance plan offers a 10% discount for getting a "biometric screening" at their preferred provider's office. It's just certain body measurements (height, weight, body fat %, etc.) and a finger stick for cholesterol levels, but it's worth the hassle for the lower premium. I'd be ecstatic if they had a day where the provider came to the office and did the checks here, privacy be damned, just because it would mean I don't have to go all the way to the edge of town for what amounts to five minutes of actual time with a doctor.
Also, I know a lot of healthy people don't even bother with annual exams and only see a doctor if they're sick or injured, so incentivizing full physicals and providing a convenient way to get them could be seen as a way of lowering overall payouts through early detection of problems. Group physicals would also be cheaper overall because the assembly line setup lets the doctor see more patients in less time at the expense of modesty, and the insurance company is ultimately a business where the bottom line is the first priority. It would never happen because of how prevalent Puritan values still are in America, but I can see it being beneficial overall if it were a thing. I have chronic conditions and use a lot of sick time for doctor visits, so even just saving one or two a year would be extremely helpful.