Many, many problems in Safari immediately after upgrade to Catalina

I just upgraded to Catalina and I am having so many problems in Safari it is unusable.

Examples:

• I cannot use private browsing. The command New Private Window in the File menu is greyed out.
• I cannot turn off Safesearch in Google search. I can on other devices, such as an iPad or iPhone and I can turn it off on the same Mac in Chrome. But not Safari.
• I cannot select Settings for This Website in Safari. The command is greyed out.
• Many web pages open with the below cryptic and completely unhelpful error message.It seems to have something to do with adult or inappropriate content. Google searches that would return such sites produce this message, as does going to and adult site which I could do before downgrading to Catalina.
• 

None of these problems occurred with Safari in Mojave. None of them occur in Safari on other dives on the same network. None of them occur on Chrome on the same computer. I have no Safari extensions.

The Content Blockers preference is off.

Please help. Every other post I have made recently has received no reply. This is incredibly frustrating. I effectively have no Safari. It is completely useless until I can fix this problem.

It seems like there’s just one elusive setting somewhere, but I’ll be ****** if I can find it and I know I never enabled it. It just came on the same time I downgraded to Catalina from Mojave.