Do I need to do future updates ? It’s quite risky, isn’t it ?
In fact, this should have been a “one off” as you could check by following some of the threads sharing this tag ota-upgrade. Many users had a successful experience, except perhaps a dozen of you covered in the list above. I think you are saying that you took the path of “going back” to Oreo - in which case, it would look as if you tried again (by upgrading to 0.21, Q, Android 10) to do the failing Upgrade.
There is no news that I have seen on the optimum fix.
SIM card is not recognized
is mentioned in this thread: SIM not detected SM-G960F after OTA Upgrade.
A https://community.e.foundation/search?expanded=true&q=Samsung%20encryption on the subject of Samsung + encryption might suggest it was best avoided without expert guidance!