You might be able to use ChromePass.

In its advanced options, you'd select "Load the password from another Windows user or external drive" and set the path to "C:\Windows.old\Users\theuseryouused" for example.

Then, you'd set what password you used for that account.

Then, you'd enable "Advanced external drive settings" and point it to the "C:\Windows.old\Users\theusername\AppData\Roaming\Microsoft\Protect" folder for example.

Then, you'd set the path for Opera's profile folder where its "Login Data" file is at. "C:\Windows.old\Users\theusername\AppData\Roaming\Opera Software\Opera GX Stable\Default".

Then, you would enable "Extract the encryption key from the following Local State file" and point to "C:\Windows.old\Users\theusername\AppData\Roaming\Opera Software\Opera GX Stable\Local State".

Then, you'd click OK and see what it does. Maybe even click View -> refresh. If there are any problems with your settings or errors getting the passwords, ChromePass will let you know.

It's a longshot though. Everything has to be perfect for it to work. Also, this won't work if you were using a Microsoft account to log in to your user account. Only works if you were using a local account with a normal username and password.

Another option might be to using Windows recovery to go back to the old installation.

Were you using Opera Sync to sync your passwords?