I just had the pleasure to not being able to use Private Browsing on my Mac since running the latest version of Tahoe, 26.3.
First it told me that Private Browsing isn't available because of a st Screen Time passcode, however that never was a problem in the past. After I disabled the passcode, it said something about a Profile or Restrictions preventing Private Browsing from working, but Restrictions aren't enabled on this Mac either.
After looking up some information, I found the only thing to wards for me is:
Systems Settings -> Screen Time -> Content & Privacy -> turn it ON -> App Store, Media, Web & Games -> Access to Web Content -> Unrestricted
Then, go back to Content & Privacy and turn it off.
That fixed it for me and maybe it'll help you, too.
First it told me that Private Browsing isn't available because of a st Screen Time passcode, however that never was a problem in the past. After I disabled the passcode, it said something about a Profile or Restrictions preventing Private Browsing from working, but Restrictions aren't enabled on this Mac either.
After looking up some information, I found the only thing to wards for me is:
Systems Settings -> Screen Time -> Content & Privacy -> turn it ON -> App Store, Media, Web & Games -> Access to Web Content -> Unrestricted
Then, go back to Content & Privacy and turn it off.
That fixed it for me and maybe it'll help you, too.