Before I start, I would like to say the new look for Reallusion Hub is great. Everything is much clearer to read and I like the darker menu theme. However, I have also noticed a couple of problems with the major update.
First I tried to uninstall CC3, where the options for this in the Hub don't seem to do anything. As such users should, for the time being, use the Apps manager in Windows 10/11 Settings. The reason I was uninstalling CC3 was because I recently got an upgrade to CC4, so I decided to install it on my newer system as well.
This led me to my second (and very important) issue. Upon clicking the Account symbol to log in on the new machine, a window pops up which should give the option to enter email and password, but it doesn't - instead you can't close this, making the Hub inaccessible. The only way to resolve it is to force-quit the Hub. Unfortunately, you still can't log in to install licenses, and I've found trying to install anything that doesn't require you to log in creates the same error...
Until a hotfix is deployed, users should uninstall their applications completely, uninstall the Hub, and do a clean install. It is the best way to avoid incompatibility between the two Hub-versions.