The problem is that Apple changed the API a bit for the file open dialog. Whereas before they allowed people to select folders with it they no longer do. OMZ will need to add the open folder dialog to the app as well for it to work properly. The author of Textastic is having to do the same thing and that app should be updated by the time iOS 13 is released. I doubt Pythonista will have the same luck.

@ccc Done, thanks and sorry, I always try to not forget it, but, my memory is often overloaded 😢

@PKHG , after you share a gist, the URL is copied to the clipboard. A HUD comes up telling you so. You can use the link item here and paste in the gist's URL.
I made this test gist. Anonymous, but not private settings.
Should would if you click the link, but its not inline as @zrzka points out.