Configuring the connection. Let's clarify all the details.

Access the router settings through your browser (the IP address for accessing the settings varies for each router model). In the settings, find the firewall and disable it; you can also open ports there if disabling the firewall doesn't help. To be absolutely sure that the issue is with the router, connect the internet cable directly to your computer. If everything works fine when connected directly, then the problem is definitely with the router.