It is normal since the phone goes into 2G mode for calling (because there is no 3G anymore) For internet the modem would need to be in 4G mode, but you don’t have VoLTE. The change is probably the dismissal of 3G by your provider.
If I got it right, this is not the case. My MNO (PT) doesn’t have 3G anymore. So, while on call, it is (and should stay) on 2G.
I once thought it had no Internet, but another time packets came through. Didn’t investigate further…
Okay, to be more precise: while being in a call only 2G internet is available (which has a very small bandwidth which basically translates into no internet). After the call ended, the device will go into 4G mode again, which means that LTE bandwidth can be used (internet works)