A couple of days ago my network connection became really laggy gaming on PS5 with packet loss and high lag. I swapped from 2.4GHz to 5GHz and that solved it. Yesterday the PS5 defaulted to 2.4GHz and wouldn't connect to 5GHz until I rebooted everything. Today, I can connect to 5 GHz but it won't connect to the internet, but I can connect to 2.4 GHz fine, only with awful Wifi issues.

I don't use smart connect. My PS5 has a fixed IP address and approporiate port forwarding. Nothing has changed on my end between it working and not.

The PS5 uselessly reports:

“Can't connect to the internet. Your internet service provider or your router might be preventing your PS5 from connecting to the internet. Make sure you can connect to the internet via the same network as your PS5 by testing the connection using your computer or mobile device”