I see an opportunity to create a slider for lightroom classic that adjusts exposure using plus and minus keyboard keys when the slider is used on the touchbar, but im unsure where to start.
You'll need a way of communicating with Lightroom. As far as I know there's no off the peg way to do this but if you're not afraid to get your hands dirty you could write a Lightroom plugin that would do the job. Use the LrSocket class, have it listen on a port and have, say, a Python scripted trigger that sends instructions to your plugin.
One way communication - plugin listens, trigger sends - is fairly straightforward. A send-reply setup is a little more complicated but it's definitely doable.
I may have made a way to do this, I will reply here once it's fully working