The /e/asy-installer is not clever enough to downgrade your S9 with stock Android 10 to Android 9. There are only a few constellations where Samsung allows a downgrade. As of bootloader version April 2020, Samsung no longer allows a downgrade even within Stock Android 10. To put it simply, the S9 Android 10 bootloader has a roll-back lock that cannot be bypassed.
Let’s look at the files that the /e/asy-installer downloads after successfully identifying the S9:
These files were already used in /e/ OS 8-Oero times of the S9 ‘starlte’. TWRP 3.2.3-0 is totally outdated, so it may still work. But why isn’t a successor used, e.g. version 3.3.0-0, 3.3.1-0, 3.3.1-1, 3.4.0-0 or now 3.5.0_9-0? New /e/ OS and old tools?! Why?
As a test, I tried to install the /e/ OS
e-latest-starlte.zip without /e/asy-installer, i.e. manually via TWRP 3.5.0_9-0 on my Galaxy S9 with Samsung firmware Android 10, build date April 2020. The result was the following error message:
After the “Reboot System” in TWRP, the S9 started in Samsung download mode. The previously working firmware became inoperable, TWRP was also unusable.
Note: I assume that the
e-latest-starlte.zip file does not yet have the status /e/ OS ROM
e-0.13-q-2021012097133-dev-starlte.zip and that is why it is causing this mess.
Well, as long as the S9 boots into Samsung Download-Mode, nothing is lost. I reinstalled the latest TWRP 3.5.0_0-0, with this then the /e/ OS ROM e-0.13-q-2021012097133-dev-starlte.zip
The result is - a working Galaxy S9 ‘starte’ with /e/ OS ‘Q’ - without
using no-verity-opt-encrypt-samsung-1.0.zip, without using
And the summary of my experience is - I don’t trust the ‘Windows’ /e/asy-installer. The classic installation method is the safest method for me, at the same time it is easy to handle.