A german manual how to install an /e/ ROM

After manually checking for an update on the device, I get a message in StockROM Android 8.0.0:

:sunny: Alter updating, you will not be able to downgrade to the old software because of updates to the security policy.

When trying to downgrade from a current Oreo 8.0.0 version 2019 to Nougat 7.0, I get the error message:

“SW REV.” CHECK FAIL (BOOTLOADER) DEVICE: 7, BINARY: 2

In my experience, Samsung’s download mode refuses due to Samsung’s internal firmware revision number downgrade from newer versions to older versions.

So how can I downgrade from StockROM Android Oreo 8.0.0 year 2019 to StockROM Android Nougat 7.0 year 2017/2018 to install /e/ OS e-0.7-n- dev (nougat)? What is the trick?