I recently took back my Fairphone 3+ (factory reset + last update) and put my french SIM Free Mobile 5g into it.
Unfortunately, no way to connect to mobile data. Wifi is fine, phone, texts are ok but the smartphone never connected to any 2g, 3g, 4g network. Of course the SIM was working fine in the previous smartphone.
I already tried many things. Changed as much settings I can think of in mobile network and so on. There are also several topics in that forum but none worked for me. I suspect it’s just an APN settings to fix but I can’t figure out what.
I made it! I read elsewhere on this forum that maybe, with a factory reset, it may work. So I tried and yes, it worked!
I made a factory reset, refused to use the wifi during installation and magically, it finally connected to mobile network! I imagine that perhaps mobile network broke at installation and it would be why it broke for me which did a fresh install recently and not for anyone which did just an update.
