Notes in MacOS Preview App.
This question was asked but never properly answered: "I often add sticky notes to my PDFs in Preview to write notes in and sometimes I write a lot in one sticky note so not all of the text is shown at once. This wasn't a problem when I was still using macOS Sierra because the sticky notes would expand as you wrote more text but now in macOS Catalina, the sticky notes in Preview are a set size so I have to scroll down to see all the text. However when I click on the sticky note and try to scroll, I end up scrolling on the PDF itself and not the sticky note."