Can't transfer Repentance+ save to another Steam account (Steam Family)

Hi everyone,

My brother and I have been playing the same save file on my Steam account for a long time.

Now we're trying to move that save to his Steam account (he plays through Steam Family), so we can each have our own profile while keeping all the progress we've made together.

We've tried:

Copying the save files from Documents/My Games/Binding of Isaac Repentance+.

Copying the files from Steam/userdata/.../250900/remote.

Downloading the Steam Cloud save and replacing the files.

Following several YouTube tutorials and old Reddit posts.

Nothing works. The game always starts with a fresh save on his account.

Is there something that changed with Repentance+? Are saves now tied to the Steam account somehow, or is there another file/location we're missing?

Has anyone successfully transferred a Repentance+ save between two different Steam accounts recently?

Any help would be really appreciated.

We're starting to lose our minds