Have you tried this?
- I'm having trouble using C&C:Online with Steam.
Solution: Open the C&C:Online launcher and use the Hook menu to hook your game.
1. Go into Steam and create a desktop shortcut for your game.
2. Open the C&C:Online launcher and go to the hooking menu. Hook your game. When Hooking, you should receive a prompt asking for your confirmation, this is how you know it worked. If you don't receive anything and the issue still occurs, check your anti-virus (Norton especially) as they are known to delete the hooking file. Add an exception for C&C:Online.
3. Launch the game using the shortcut Steam made for it on your desktop (if you don't have a shortcut, go into Steam and make one). The launcher should pop up, so select your game and off you go
Else it might be some firewall, try adding an exception in your firewall.
If it is a problem with ports, try using a VPN. I have found that ProtonVPN works and is great.