Okay Tom, thanks for sharing your experience in clear presentation way.
I’ve tried several installation variants, but certainly not all of them. For example, when flashing /e/ OS ‘Q’ on the Galaxy S9 and S9+,
I did not use no-verity-opt-encrypt-6.1 (exception: GSI ROM installation),
but successfully already used TWRP 3.5.0_9-0
On the Galaxy S9+, I also successfully installed eRecovery as an alternative.