No internet via LAN despite internet access. What could be the problem?

My problem is the following, namely that my computer has internet access, but can't access any pages, and can't connect to other services (Steam, virus protection, etc.).

To rule out the cable as a problem, I connected my laptop to the LAN cable. Everything works perfectly here.

Regarding the cable, one should say that I switched from a rancid old LAN cable to a CAT6.

Look at the proxy settings…

google times for "proxy settings" in connection with your operating system