Cannot change Safari homepage - High Sierra

Howdy,

Just got a new iMac 21.5 3GHz to replace our mid 2007 20". I've used Migration Assistant to move everything over from the old to the new, but the home page setting didn't come across and it will not let me change it. No matter what I do it reverts back to https://www.apple.com/whatever.

I do not have profiles enabled, and only have one user set up on the computer. That user is the administrative user.

I've tried the trick of entering in the URL for Google, not tabbing out of the field, and clicking a different icon in the top bar, but that doesn't work. Clicking use current page _always_ just puts the Apple URL back in.

This seems to be a pretty common problem that I cannot find a thread which gives a definitive answer.

Any ideas? TIA