Preview Annotations and Highlights – disappearance

Why do most annotations and highlights made on a pdf and saved to either desktop or external drive disappear when the file is opened later?

There was a lot of discussion on this in 2022 (for OS Monterey or earlier) and several complex solutions (which tended to assume that there were issues with "well-worn" file directories etc).

But I encountered this issue on a brand new device with latest OS (13.2). Why does the problem persist? (It isn't one I've ever come across in years of using Preview prior to advent of Monterey and Apple Silicon).

The "solution" I stumbled across was to export the file to pdf format (yes, pdf) but select "Create Generic PDFX-3 Document" in the Quartz Filter menu. All annotations and highlights are visible when the file is re-opened in Preview (or a 3rd party app like Adobe Reader). But what a rigmarole.

How many users are out there thinking they've saved hours of work... only to find it missing later? If the annotations are still present when saved as a regular pdf (no quartz filter etc) but somehow hidden, could Support please explain how they are recovered without (e.g. rebooting the machine in Safe mode)?