Can you try this?
Use command:
~/umbrel/scripts/app restart btcpay-server
Then wait a moment after this completes then System > Restart or sudo reboot
Then please wait 5 minutes, could take a while longer maybe, then it should work normally! It should go from Starting like you have now to clickable, then give the Umbrel page a few minutes to load the BTCPay Server login page again. This has been successful to get it working, let us know if it works for you or we can continue to troubleshoot!