How to make a plugin for Discord (like vencord and betterDiscord) Setup guide or code?

We are NOT trying to make a plugin for vencord or betterDiscord. We are trying to make an actual add on/plugin for Discord itself. Meaning users will go on the web and install our app, once installed the Discord app will have a different look to what it usually looks like. We just want to know how we can achieve this, how do we use electron and js injection to alter the look of discord itself. This isn't exactly a 1:1 problem, but even a bit of guidance would help. Me and my developer are having a tricky time figuring out how we can make an add-on to Discord We're solely making a simple Discord plugin that could benefit user experience. It is not a client, or discord modification app similar to Vencord and BetterDiscord. It is just going to add a few little buttons to the actual Discord app (on macos and windows) We know it's something to do with electron and js injecting but we really need a bit of a lift off as we dont know where to start when it comes to coding and actually testing our plugin on the Discord application. How do we actually run and test our app, and make it work? We've tried a few things, we've looked through the source code of betterDiscord and dmed developers but no one can help us. We really just want to make a simple plugin to benefit user experience on discord.