Custom browser protocol to handle opening windows desktop application from the browser w/ xdg-open

Discord and Zoom do this. There seems to be no documentation on this but a lot of sites use this. I got a bit of help from reddit with the keyword "custom browser protocol" but I don't see any docs that would help me in my case

The software I want users to be able to open is a Windows desktop application built by the client (whose projects I've inherited) which will definitely be on users' computers. These are Excel projects

Any help is appreciated, thanks