Hi Noris,
I tried the steps as you suggested, but the same problem. (I am not running the server on macOS at the moment, so the steps applied only to the Roon Remote that used to work fine fetching data from the Roon serving running on my Synology NAS.) After rebooting, the Remote gets stuck in the same state as shown in the screenshot originally submitted with the ticket. I left it for a couple hours, and nothing changed.
To provide a bit more information, I have looked into the log-files from Remotes on my two Macs in interacting with the latest version of the Roon server on the Synology NAS. The Roon Remote on my MacBook, MBP14, successfully connects to the server on the NAS and displays my Roon library off the database also hosted on the NAS. The Remote on my MacStudio, however, fails, even though it seems to communicate with the server at least partially. I have documented these detailed observations here. Hopefully, this may help locate where the Remote fails to close the Connect panel and move on to display the library on Mac Studio.
I will wait for your suggestion for the next step.
Seungoh