MrSquid

Thanks Callum - unless I'm missing something, everything mentioned in that thread is all the items I mentioned in my post that I've tried. One other thing in case it helps. Not all files save out of Designer with a file extension. If there is no extension, it seems like it always shows a preview. If there is an extension, on some files there's a preview and on some there isn't. And again, this is on 2 of 3 computers. The 3rd shows all previews just fine.

We run Designer on 3 Macbooks, with all files saved on the same Dropbox account. One of the computers (10.14.6 Mojave) shows previews of Designer files just fine - both in normal Finder browsing and just through CMD+O in Designer. The other two (10.13.6 High Sierra and 10.15.4 Catalina) only show the Designer icon - no preview. Sometimes the High Sierra machine will show a preview if there's no file extension showing in the file name. Both the Mojave & High Sierra machines are running AD 1.6.1, and Catalina is on 1.8.3. We've done the basics with the High Sierra & Mojave machines like CMD+J in finder and making sure show icons & show icon preview are on. We've made sure that they all open with Designer. And of course the "Save thumbnails with documents" is checked in Designer's preferences. Thoughts or suggestions? We've tried to cross check as much as we can against the Mojave machine since that's showing previews perfectly, but we still haven't found the magic bullet. And I should point out - we're not trying to preview files within dropbox itself via a browser. 99% of the time we're just trying to preview while opening files right in Designer. Once in a while in Finder, but mainly within Designer.