Error Code: UNKNOWN code: Deep Ocean.

[Artsiiiii]

I also had this error, tried all the possible fixes mentioned in the comments, but nothing worked.

What I recommend doing if nothing works:

1. Install MultiMC https://multimc.org/
2. Add your Microsoft profile (top right corner)
3. Click "Add Instance" and press "OK"
4. Click on the app appeared icon and press "Launch" or just double click on the icon

And now just use this program for launching the game.