Copy pasted from pinned messages in the Duelists Unite Discord #tech_support channel:
Again to all of you that are having issues. Try the omegaupdater first. If the omegaupdater has an error, it is because you put the game in a folder that has no write access. That’s why the default location was C:. You moved it to a place that’s not writeable. Right click the folder and properties. Untick the Read-only. Then it will work and can write over the ygo omega.exe.
As for Windows 7 users, it’s because you are lacking .NET updates so you can’t use omegaupdater. Either upgrade to 10 which is free or find .NET and get all the updates.
Same goes for uninstalling. You guys moved it from C:, so the uninstaller can’t find the game.
If you are stuck at the loading screen, you can close the game using ALT+F4 and run the omegaupdater. It will do the same thing.
more than 90% of the problems are fixed if you run omegaupdater from a writeable folder.