When a firewall or network router is blocking LR's network requests, there's usually a different error message than what you're seeing. Nevertheless, try these troubleshooting steps (or try them again, just in case):
- Temporarily disable all the firewall/anti-virus/security services on your computer. If that solves the problem, then add a specific exclusion for LR to the services' rules.
- Connect to another network, preferably one serviced by a different ISP. E.g. a Wifi connection of a neighbor, a coffee shop, work, or your phone's hotspot. Sometimes the routers in these networks block LR's requests, especially in authoritarian countries like China.