I'm a Y7 tutor in a school that will have a similar policy when students come back. I honestly don't think it will be that disruptive to friendships. I think stopping and restarting school (perhaps multiple times) due to cases within the bubble or high levels of teacher absence would be FAR worse!
I do accept that there are other factors involved, but we can't control what happens outside of school, only in school- BUT we can't control that! I do think communal areas present some risk- our school canteen is not well ventilated and lacks space to social distance, but it's our only option for serving school meals. The alternative is probably having the canteen shut, no hot meals, and a packed lunch made daily for FSM children. A lot of parents would be unhappy with this, too.
FWIW, most of the students' social time will be spent outside (before school, break and lunch) whenever possible. Masks won't need to be worn outside.
I think this year will be tricky socially for lots of children for lots of reasons, and we will do our best to help with that, and I plan to do lots of pastoral work during tutor times. That said, I don't think wearing masks in the corridors or in the canteen queue will make much difference? Everyone will be in the same boat and kids are adaptable. We have worn masks in school on results day, and for staff training, and it is still pretty easy to recognise other staff. He'll get used to it!
I do think if you go in with a "this is dreadful" attitude, it will rub off on your DS, even if you don't say anything to him. That won't help him with starting a new school. It's normal to be worried about how he will cope in Y7, especially this year, but he will be ok!