I do not know the device. Did your downgrade method include a Factory reset ?
If not perhaps remaining traces of Android 13 are an issue. From your current position
fastboot -w
might allow you to move on.
No, e/OS + Android OS version names and numbers? - #3 by aibd I expect you did already, but you could double check that you have the latest revision of Android 12.
Late edit in light of solution below, Android 12 (s) manufacturer firmware should be the correct starting point for any /e/OS-s build. However some as yet undefined problem is still preventing a standard install method for e-1.12.3-s-20230628304336-dev-bramble.