There was a discussion a while back about the "Preferred Network" option being hidden in Android 10 when on Fi or something like that, but it seems to be back, and I needed to use it to force 3G just now at CDG (outside of WiFi range, waiting for boarding to complete ) -- status bar indicated LTE and Signal Spy said I was connected to "S.F.R. LTE" but there was no actual data service. Downgraded to 3G and now it has me on S.F.R. HSPA+ and working data.