I spoke to the technical support person assigned my case, today. (He did not receive my replies to his messages, but luckily called me anyway, hence the long delay?)
The technician confirmed that my Telco’s mobile data and my sim card were configured correctly (no errors on the Telco’s side).
The technician said that the problem (greyed out/blocked options) is because eOS has "not applied a patch correctly".
We tried some other tests like: “reset network settings” (reset WiFi, mobile, bluetooth in eOS), but when I tried to do this an error message appeared and I had to close the window: another blocked setting?
The technician’s advice was to update eOS, download a new setup file and reinstall it
I refreshed my updates and my phone was up to date:
31 May 2021
Last checked: 26 July 2021 (1:39 pm)
I will try to reinstall eOS first.
If I still have problems, I would like to try the manual option you are suggesting, smu44. I know the Teamwin Recovery Project (TWRP) screen options and Android Debugging Bridge (ADB). I was in and out to them trying to get eOS installed - maybe, this is why I have these problems, lol? Honestly, I don’t know how I haven’t bricked my phone yet?
Btw the “preferred network type” is LTE only in Australia.
Also the APN settings were not correct, so I do need to edit them to be able to get mobile data.