[Renate]

You must defeat the anti-rollback mechanisms to load something older.
The problem is also that some file structures might have been upgraded already.
There's no guarantee that older firmware will work.

I suggest that you first make a full, raw backup using EDL (64 GB).
Then you'll need to install a custom recovery to install the older firmware.
If things do not work you can restore the backup.
Never do a "factory reset" or a "wipe user data".