Fairphone 4 cannot receive network

My Fairphone 4 cannot find any networks. I've tried multiple simcards which all work in other phones but in the Fairphone 4 they cannot find any network. Could this be a problem with the antenna? Or a software problem? I think the antenna is included in the rear camera module, so I could replace that, but I would like to know for sure if this is the problem before I do.