Checked out the videos and it as impressive.
https://sioyek.info/

It appears that bookmarks and highlights are stored in a sioyek database rather than as part of the pdf itslef, but I think that is where the power comes from.

Here is a overview from youtube
https://www.youtube.com/watch?v=w9gm6Me7tLM

Nice find, thank you very much, looks interesting - on my list for the weekend.