Check if Windows Defender Controlled Folder Access feature Ransomware protection is enabled. If so, configure it to add Quicken as an "allowed app" without turning off Ransomware protection. Perform the last step in https://community.quicken.com/discussion/7857675/faq-windows-defender-controlled-folder-access
Are you getting "Oops, something went wrong"? Have you recently enabled a VPN? If so, this might be the problem. Try turning the VPN off and see if that helps.
Is there a corporate or otherwise external firewall getting in the way? Contact the IT people maintaining the firewall and ask for permission.
Does your Antivirus software allow Quicken to connect to the Internet? Quicken needs to be able to establish outbound Internet connections for the program to work.