The short answer
You're treating burnout with the thing that caused it — more work. The first move isn't to find joy again; it's to stop the drain. Deliberately doing less, even briefly, is not laziness. It's the only way the signal for what you actually enjoy can come back.
You keep working harder hoping to outrun how hollow things feel. Research on burnout consistently shows that when demands stay high and recovery never comes, the ability to feel reward or pleasure gets ground down — not because something is permanently broken, but because the system has had no chance to reset. The flatness you're describing is a predictable result of that pattern, not a character flaw.
Marcus Aurelius put it plainly: stop roving and wandering to and fro, and give yourself the quiet to learn something good. He wasn't talking about vacation. He meant: stop the restless motion that feels productive but isn't. More work as a response to burnout is exactly that restless motion — it keeps you moving so you never have to feel how tired you are.
This week, pick one 30-minute block each day and protect it from work entirely. Don't try to 'find joy' in it. Just sit with no task. Walk. Eat without a screen. The goal isn't to feel better immediately — it's to stop adding to the drain. If the flatness feels heavy or hard to carry alone, talking to a counselor or therapist who works with exhaustion and overwork is worth considering.