Not Op, just want to chime in that sadly these days a lot of keyboards and laptops come without the context-menu button.
There were even some Logitech keyboard that would use the "context menu" button to trigger a right-click (where the mouse cursor was) instead of opening the context menu (of the currently focused item)
(Shift+F10 works as context-menu on some windows computers, but not all. Not sure if it comes down to Windows versions or different hardware)
Another option is subpaths: xyz.ddns.net/portainer
Just one open port, to your reverse proxy (nginx or other).
The client updating no-ip with your dynamic IP is independent of the reverse proxy software.