To make NodeCanvas and/or FlowCanvas work on AOT platforms (like WebGL is), you need to please generate the AOTClasses and link.xml files which can automatically be done so through the Preferred Types Editor Window.
Please take a look at this documentation section -> https://nodecanvas.paradoxnotion.com/documentation/?section=working-with-aot-platforms
Let me know if the above helps and works for you.
Thanks!