In short: NEVER save a PDF with Preview. You should probably just avoid opening it in Preview period, frankly.
Exactly this.
So the question is, whose responsibility is it? Apple’s to magically support the intersection of all the broken sofware?
You essentially have argued that ABBY is popular enough that Apple should have tested it.
Maybe it is popular, but the implication is that Apple would need to regression test against all this popular PDF generating software for any change to the preview engine, since they wouldn’t be able to know for sure what software’s PDFs would be broken by conforming changes.
What we know they did, was to make a copy of Big Sur available for ABBY to use to test their own software. That’s pretty standard practice in a case like this and is them behaving responsibly.
If Preview really was at fault, ABBY could have raised the issue with Apple, and or put a warning in their own software. If it’s that popular, you’d think they would have an incentive to do this.
What isn’t obvious is that Apple should somehow introduce workarounds every time a third party doesn’t fix a bug.