I've love both Firefox and Okular (KDE's evince), and both "technically" support PDF inking, but the experience is just subpar to what Edge offers now for notetaking and reviewing articles. Xournal++ is the gold standard and fully supports my Surface Pen, whereas Edge does not recognize pressure or the eraser. However, I work with a lot of embedded files (Logseq), and the fact that Xournal++ cannot bundle a PDF in a single file and instead needs a reference, plus the fact that PDF is a universal file format, makes Edge the most enticing option for now