I had exactly the same problem. I followed JordiCS99 suggestion, connect via VPN and Safari works again. I could also connect to Apple Store. But this is not a definite solution, just a temporary one. And we would appreciate if Apple could help us solve the problem for good.

Hi. The same happens to me. And I cannot believe Apple does not fix it. The whole thing is useless and you cannot reverse and go beck to Catalina. Terrible, terrible. Never experienced anything like it. What are they doing??!!

Again, JordiCS99 solved my problem with the "automatic proxy detection" solution. Thanks for that!