Which of these should be contested and which should be validated?

Identities don’t really need to be either validated or contested, especially if the person didn’t ask for it. Validation will likely win you more friends, though.

Obv use their preferred names and pronouns to be respectful, as with any person. But beyond that, there’s really no need to get involved in their identity at all. It’s a deeply personal thing and it’s unlikely they’ll change it for anyone other than themselves.

The big symptom unique to burnout is anger. Ultimately leading to blowing up at coworkers. If you’re not experiencing that it’s probably not burnout.

Depression and ADHD might be good thing to check for.