I know this isn't your mod's problem, but maybe you could contact the developers and discuss about a better implementation on their side?

Since Sodium replaces the video settings screen, there's not much we can do. It would take significant work on the author's part to change that for a small mod like Boosted Brightness.

I can add keybinds to raise, lower, and reset brightness. What do you think of this solution?

Looks like Sodium is going to provide an API for this in the future: https://github.com/jellysquid3/sodium-fabric/issues/414#issuecomment-739527013
Pull request: https://github.com/jellysquid3/sodium-fabric/pull/293

But until then, a keybinds solution would be fine I guess 👍

Using Java Reflection you can manipulate almost everything (actually quite amazing and interesting what you can do with it)
Its a bit dirty but it works, here my pullrequest: #9