If you're using Windows Hello and have a pin, I think it wants the pin. If you're not using Windows Hello and just have a regular login for a local user account with no password at all, I think you can just press enter on the blank field. If you're not using Windows Hello and have a regular username and password (Microsoft account or local), you need to put in the password.
replace password
If you change your password, there's a good chance that Opera will no longer be able to decrypt your stored passwords to show them to you and allow you to export. Did you try the new password in Opera? If if fails, you might (long shot) be able to change it back to what it was exactly and then try that password. No guarantees. Same if you have to go back to using Windows Hello and a pin. If you use the same pin as before, there might be a chance if you put that pin in Opera, but no guarantees.