I’m specifically looking for something that can both add text and works well with a stylus + tablet (specifically a surface pro). The best I’ve been able to find is Okular, but it’s been very finicky for me, especially while editing text. Is there anything better, or does what I’m looking for just not exist yet?
Xournal++ if you need to edit pdf, Rnote if you need to take notes (it has infinite canvas like onenote). You may also want to check Krita, it is primarily a drawing application, but can draw on pdfs as well (not very practical tho)