It sounds like his testosterone is not returning. You should definitely get a test testosterone test to find out what the level is. I used to get terrible hot flashes from ADT, Fortunately, they have pretty much stopped even though I am still on ADT and my testosterone is really low. I used to wake up at night with the sheet wet under me, That stopped with the device I mentioned below.

If he continues to have hot flashes, and it turns out his testosterone is very low you could get testosterone injections, which would raise it so that the hot flashes would go away.

I use an Embrlabs.com Wave 2 Device to stop hot flashes. I’ve used it for over five years. One of the best features is, it has a night mode which last seven or eight hours and really stops the hot flashes and hot sweats at night. You can get one to see if it works, they have a 60 day money back guarantee. I have instructions for configuring it for ideal usage. If you get one, you could put a message in here and I will give you those instructions. I beta tested the device a few years ago and also work with them on any fixing bugs in their Software.