Posting this so that hopefully it helps some of you having the same issue I had. I contacted NAMCO about this issue of a never-ending loading screen (game won't work).

First, they told me:
"We advise you to disable the cloud saving option, then to remove the current save file and to try playing again."

This did not work for me, so then they suggested this:
"The game stores local configuration information under the path:
C:\Users\<Name>\AppData\Local\BANDAI NAMCO Entertainment\katamaridamacy\Saved

Under Saved you have two folders - SaveGames and SaveTemporary. The SaveTemporary file is where system configuration is stored, inside the files called input.setting and quality.setting

Please delete those two files. Restart the game and try playing again. If necessary, please reinstall the game."

After I did that, the game FINALLY worked! I didn't need to reinstall it.
I hope that maybe this helps some of you, since I had a hard time finding anything out about this issue. If you tried everything else and this still doesn't help, NAMCO's customer service is excellent but you will have to be patient.

Thanks NAMCO!