I’d like to provide an update here.
I’ve followed the instructions again as on the installation page was provided.
The result was the same. Same errors, same ramdump.
I did manage to boot /e/ 1.2 twice. It was not a pleasant sight. screen input took almost 60 seconds to be recognized, for each input. The first boot wizard crashed several times.
I remain with my belief that the vendor_boot linked on the installation page will not work and is not intended for Android 11.
LineageOS, where the vendor boot comes from, currently only supports Android 12.
I did reach out to the LineageOS community and asked for help or archives of older versions of vendor_boot, but unfortunately there are none.
Useful tips I figured out along the way:
Android 12 beta page provides a downgrade to Android 11, but no upgrade path from there: Android 12 Developer Preview Program | ASUS Global
Android 13 beta page provides a downgrade to Android 12, which in turn can be upgraded to the latest version or downgraded to the latest Android 11: Android-13-Beta | ASUS Global
When the ramdump error appears, let the battery drain until it’s certainly turned off, then charge it to capacity and booting into fastboot should be fine.
I’m now reluctantly running LineageOS, because I do need a phone. I’ll be following this project closely. The past 3 years I’ve been on /e/ I’ve always been very happy with it and I’m looking forward having it again, albeit under better, less stressful circumstances.
I’d like to thank all repliers in this thread for their help and insight. I’m also very grateful towards everybody who is making /e/ a thing!