I have 3 Macs and I have the same issue in 1 of them.
The one that has this issue where is not storing any passwords is a MacMini with M2Pro.
I tried to export the password from one of the working Macs and import to the one that is not working and doesn't work. I tried to add the password manually at the settings page and doesn't work either.
Is not an issue with the Apple Silicon since one of the working Macs is a MacBook Pro with M1Pro Opera updated to 96.0.4693.20 (arm64). The other working one is an Intel based MacMini.
Waiting for a swift solution from Opera...