You can use any text editor, e.g. kate, open a terminal and use typst watch document.typ or simply typst w document.typ and have any pdf viewer at the side. It'll auto update the new output in real time.
Your screenshot actually shows the webeditor of typst.
Currently, it is a little bit difficult to find. There is an android and a different ios marknote app. KDE’s marknote app still has few stars on github