Hi John,
Oh gosh.....it's just been a few messages like yours that I see from time to time (over probably 8 years since I first heard about it). And some were on the mailing list (i.e. hard to find unless you have mad searching skills). I can't recall exactly what the solutions were, for the others who had this problem.
I would think that putting everything back to where it was before, and of course with restarting the whole system, should fix it.
As far as I understand, a fix for the high dpi screens is coming in the next major version release. But high dpi isn't the same thing as high resolution, is it?? I don't know about the multiple screens. Let me search the bug tracker....
This one is on Windows:
https://bugs.launchpad.net/inkscape/+bug/555253 Until I saw that, I thought it was Mac issue. But if it happens on other systems, that might point more to Inkscape, I guess. Although it's probably too complex of a problem, to minimize it like that.
This one starts out about Windows, but there are some comments about Mac issues as you read through:
https://bugs.launchpad.net/inkscape/+bug/379463Here's one about Macs:
https://bugs.launchpad.net/inkscape/+bug/1110090OH! Jackpot!!
https://bugs.launchpad.net/inkscape/+bug/1244397I won't go any further after finding that one! But for all of these, be sure and follow all the links, especially links to related bug reports. Also, note that often fixes for a lot of bugs can be very short, almost offhand comments. So you need to read them very closely, and follow the links. (Developers don't like a lot of chit chat, and tend to say volumes in just a few words
I'll have to mostly leave you on your own with those, since they are mostly over my head (plus not being a Mac user). But if you should need more answers, I'll refer you to developers.
You can reach developers most reliably via the Devel mailing list. Or actually, the Devel list is full of hackfest mail lately. You might be more likely not to get overlooked, if you post in the User mailing list. Most developers monitor both lists. There is a development IRC channel, but the person who has your answer isn't necessarily going to be logged on when you are. Find info on both of those from here:
https://inkscape.org/en/community/Or if it seems to fit with the discussion, feel free to ask a question or comment in one of those bug reports.
And I don't mean to imply I won't answer you. I'll always try. It's just that likely I won't be much help. But definitely ask and I can at least point you in some direction....probably.