Hello!
Thank you for making a bug report.
This sounds like a variety of problems that are commonly discussed on the #tech_support channel of the Duelist Unite Discord server. If you are not a member there, I recommend joining the server and reading the #rules channel to get access to the rest of the server.
That being said, there is an issue that has been common with Unity games where you have issues running in Windowed mode. You can work around this with a quick fix that is described at the following link, but it will never be perfect and running in Full screen mode is extremely recommended.
See Case #4: Installation and Troubleshooting Guide
Additionally, the game has been updated multiple times over the past few weeks and it has become a requirement to run the OmegaUpdater.exe in order to get patched to the newest version. It also is necessary to get the newest Game Server IP which has been changed recently. You can find out the steps to do this and get up to date by reading the #Announcements channel on the Discord server.
See Announcements channel here: Discord
If you have any questions, feel free to reach out on the discord to #tech_support and they will be happy to help you work through any other issues you may be experiencing with the game.
Thank you!