And the only way to stop Avast and AVG from forcing that thing is by disabling web shield which is not a good idea, right? I do not want Avast to tamper with my browser. There are many better options available now, so I do not have to worry.
No, you can just disable the enterprise policy. I also think (because I am not on a PC using AVG atm) that you can disable all this entirely by disabling the option to scan QUIC protocol in the web shield settings. If someone is using AVG, give it a try - disabling QUIC scanning should mean the AV will disable all of that policy enforcement upon the next restart.