suddenly, I can no longer preview glyphs files in the finder using quicklook, is this a new feature of glyphs 3, or do I have to do something more?
Do you have Glyphs 2 still around? Sometimes, quicklook picks up the quicklook plugin from the older version or gets stuck otherwise.
Can you try this: How to Clear Quick Look Cache in Mac OS
And also run
tried that, not fixed it. should I throw Glyphs 2 away?