Context menu for external script

I was wondering if there was something available where you can create context menus based on MIME type that can run either run a local script or upload the file to an external web page. So, something similar to the “workflow external script” app, except it runs immediately and only when you manually select the context menu to do so.

This would allow people to relatively easily make their own custom tools for Nextcloud, without the need of a purpose-built app. For example, you could right-click on a video file and have it convert to a different format. You could right-click on a group of files and put them in a compressed archive. If a website can have files $_POST’ed to them, people could create their own tools without the need to lean Nextcloud’s API.
A potentially helpful feature would be a way to see the terminal output of the program, if needed.

Here’s my use-case where this would come in handy:
I have a web-based VNC client, which allows me to access programs on my server through any web browser, from anywhere. Using the “External websites” app in Nextcloud, I can actually integrate the VNC client into Nextcoud.
There are certain files I’d like to be opened with standalone programs, so it’d be really handy if I could just right-click on them and select a custom context menu based on their MIME type, which will then automatically open the file in the appropriate program, which I can then access through the VNC. The cherry on top would be if the VNC could automatically take focus, too.