A minimal Screenrecorder based on the MediaStream API
A modern browser, preferably Chrome or Edge. Take this as an Guideline:
MediaDevices.getDisplayMedia() Browser Compability on MDN
Pretty straightforward, either host it on a webserver, both files on the same path, and open it in your Browser.
If you dont have a webserver at hand, put both files in a local dir and then open index.html
in your Browser.
After that Usage is pretty straightforward, considering there are only three buttons. :)