I’m not going to pick through his last year’s posts and make a diagnosis, but if you’ve seen no evidence of that, I think you’re wilfully ignoring the signs.
Ok, I'll continue "ignoring" evidence you can't even describe ("He talked somewhere about..."), much less cite.
For all we know his frequent absence is down to a great work-life balance on his part.
Irrespective this thread is not about who is or is not burnt out, it's about how posts like your are what enabled the xz backdoor to happen.