[mattgreenrocks]

> The company has grown to 200+ people and I'm struggling to see how my skills apply to my role since my first role is now no longer relevant to our core business.

This is the type of situation that fosters burnout. The conditions were already there ("work is a never-ending treadmill of tasks which don't interest me") and you don't see how the things that intrinsically interest you align with the business anymore, so your brain says, "I just can't."

In your shoes, I would:

* ask around about lateral moves to something more interesting within the same company, or even a downward move. If they balk that your pay needs to decrease, then you can either accept it, or negotiate a shorter workweek.

* simultaneously: start a low-key job hunt to avoid the feeling of being stuck calcifying further.

If things are really bad, consider cutting your hours, doing less within your hours (and using the extra time to take care of yourself), or taking a sabbatical if you have the means.