Just to make sure there's nothing corrupted in Opera, I'd goto the URL opera://settings/addresses, disable "save and fill addresses" (this will clear your autofill but not anything at the URL opera://settings/passwords), goto the URL opera://about, take note of the "profile" path, close Opera and delete the "Web Data" file in the profile folder (to have Opera create a new one).

Then, when you start Opera, goto the URL opera://settings/content/all, type discord.com in the search field and click "clear displayed content". Some sites save and restore autofill data themselves view cookies or local storage.

Then, goto the URL opera://settings/clearBrowserData and clear "cached images and files" for all time.

Then, goto the URL opera://settings/addresses and turn "save and fill addresses" back on.

Then, log in to Discord again and then see if you still have the issue. If so, again, inspect the text field with developer tools to see if the site did something wrong with the type for it.

If you don't want autofill for text fields and all, you can keep "save and fill addresses" disabled.

Yeah, and it suggests things that it shouldn't, like the login e-mail. When I press enter after searching it will ask if I want to save the "password", and when it's suggested later, it will show like if it was a username or e-mail with a password. It really makes no sense.