I updated my FP3 to Android 10 yesterday and lost data connectivity after the update.
I had to look up my provider’s APN and set it manually, it was no longer present in the list of APNs on my phone. I got 4G up again after saving the APN.
(Usually this is set automatically when you put the SIM card for the first time, seems like this time the update wiped it and it did not set automatically again)
Hoping this helps someone, this thread came up first on Google with the search “fairphone android 10 no data”