Galaxy S8 SM-G950F "only official released binaries are allowed to be flashed (recovery)"

[aibd]

Is there anything in the history of the phone that could be responsible for the phone still showing RMM Prenormal ?

Please open the linked topic where a number possible issues are explored.

@aibd

KG or RMM State Prenormal

In the examples below RMM refers to remote monitoring by Samsung . So if Prenormal is triggered the device will require to be online (probablly with an activated SIM card) and (generally) in normal use, in order for the remote to be checked and for Samsung to release the device. As we see below the behaviour can be quite different depending on why the lock was applied.
…
Prenormal is a “conditional” partial lock which will allow the phone to be used as normal user, but locks the bootloader. This prevents the flashing of /e/ or a custom ROM.

Could it be (from anything you know about the phone’s history) that Region lock, Carrier lock applies or might the phone be an

@aibd

Imported device

In the case of a Samsung phone sold in a non-intended market, say a European or Asian market device somehow imported to USA, then the above Regional terms can never be met (by official means).