Sorry if you read my post before this EDIT. I was wrong in what I was suggesting.
However it appears from your posts above that you may not have flashed the required additional partitions before flashing recovery:
fastboot flash dtbo <dtbo>.img
fastboot flash vbmeta <vbmeta>.img
In the eOS install guide it says:
"First unzip the /e/OS Recovery file linked in the section marked Downloads for avicii . The following files would show up in the location where you unzipped the contents of the eRecovery zip file
dtbo.img
vbmeta.img"
Well, there is no recovery paired with the latest 1.5 for S stable. In the weekly development updates they mention a problem with making this work for the T builds and suggest a solution for extracting the required .img files with payload dumper go. Looks like same problem for this S build.
Yet another EDIT: I downloaded e-1.15-s-20230913330639-stable-avicii.zip and extracted the payload.bin. Then extracted all of the images via payload dumper go just to check if there was a recovery.img inside. Yes there is . So if you did the same you should be able to get a working recovery flashed for installing the latest stable S.
As I already have the images I could post them on my cloud if you like.