Madden NFL 21 - Cannot connect to EA servers - Check Ethernet Cable Message

I know it's too late, but i had the exact same issue and this is the only thing that worked:

You simply have to port forward with TCP/UDP, the port numbers are 443 for both TCP and UDP. If you don't know how to, you just have to search a tutorial for your particular router model.

For more detailed info, just check this: https://help.ea.com/en-gb/help/faq/opening-tcp-or-udp-ports-for-connection-issues/