Lightroom 7.3.1: Annoying move to Sync when creating a virtual copy

No problème with french language and CH QWERTZ keyboard.

No problems on my Mac either. Maybe you have remapped something?...

 [CMD]+[ ' ]  produces a Virtual Copy and no Sync dialog. 

However, if you pause Syncing in the Identity Plate pulldown, and then hit  [CMD]+[ ' ], I do see a syncing dialog - regardless of whether the image or its virtual copy is synced. That feels like a bug to me too.

I just tested, I disabled synchronization in the Identity Plate menu, still no problem with CMD + '!
There must be a problem in the file defining the keyboard!
I passed my LR in English without changing the keyboard (CH QWERTZ) and still no problem.

Same here. Pauzed or Synched, Cmd-' only creates a virtual copy as it should.

It is possible you have checked the "Do not show again" option at some time in the past.