Not entirely. I was randomly poking around my old library, and discovered that highlights are displaying perfectly readably on some files, but invisibly on others. I started looking at the files themselves (using the "show file" option) and, so far at least, it appears that files I annotated in the summer of 2021 are showing the nearly transparent manner described above, while files I annotated in the summer of 2022 and later are rendering fine.

I haven't dug around to narrow the date range, and I don't have a record of when I did version updates, but it appears that this may be limited to older annotations. So it is not (best I can tell) related to the thread @poettli just shared.

But your annotations in the screenshots show a lock, which means they have been created externally. Not by Zotero. So it is covered by the thread I have linked.