Another thought:
If (Remote Monitoring and Management) RMM Locked or you can not see OEM unlock options in Developer options. RMM will prevent us from installing custom recovery and custom ROM as well as preventing rooting.
RMM features a lot of samsung firmware updates starting in January 2018. It also does not exist on all models samsung galaxy.
To find out this feature exists or not in your samsung galaxy device by enabling Developer Options. If there is no OEM unlock option in Developer options it is possible that the feature is on the samsung galaxy device in locked state. This means you can not install custom recovery such as TWRP recovery and custom ROM.
Make sure your phone isn’t RMM Locked.
I would like to downgrade Android 8.0.0 Oreo to StockROM 7 nougat and then install TWRP-for-herolte and /e/OS e-0.7-n-herolte. But of course there is always a certain risk …
Let’s wait for an answer from @donut3. He probably flashed his Samsung S7 successfully.