LibreOffice Draw can do markup and much more, the downside like OP mentioned is that sometimes the formatting of the PDF can get messed up so it's a bit hit-or-miss.

Beyond that try Firefox (yes the web browser), its PDF markup capabilities are way better than you'd expect and the PDF formatting tends to stay intact. It's probably better than LibreOffice for simple markup stuff, I just wish Firefox included a way to draw straight lines/arrows and shapes (circles, squares, etc.) to complete the markup toolbox. It does have a pen and highlighter but drawing an arrow via mouse looks a bit janky, LOL.

If you do a lot of the same type of markup (say an arrow pointed right) you could probably just save an image of an arrow and keep pasting it into the Firefox PDF editor, it'll probably look better vs drawing them out.