" as an occupational phenomenon"
"feelings of energy depletion or exhaustion;
increased mental distance from one’s job, or feelings of negativism or cynicism related to one's job; and
reduced professional efficacy"
Yes it can be occupational, but it can also be applied to home, location, country or life.
When thinking about being burnt out by life, its more commonly known as suicide but not the only reason for suicide.
When thinking about being burnt out by a country, its seen in a variety of ways, like not voting for brexit if you are british and relying on the EU to draw up the legislation, which may or may not be enacted in full. It can be the culture of the country, the way people did/do things because its always been done that way.
When thinking about being burnt out by home life, I think most parents can relate to that, but social conformity means they must maintain a stiff upper lip!
Either way, I take everything people in authority or expertise or both say with a massive pinch of salt. I've seen so much hypocrisy its laughable.
On the point of inability to relax, calcium has a massive stimulatory effect[1]. Sodium (too little or too much) also causes a rise in osteoclasts which release calcium from the bones.[2,3] And there is so much salt in the processed food today (dont think I need to provide links for that), and water hardness is a contributory factor (dont think I need to provide links for that), beit soaking in the bath, having long showers[4], or drinking lots of hot beverages, is it any wonder people cant relax? If you get banged up in a mental health hospital, you wont be eating processed food, so your sodium intake will likely fall, and they probably filter their water so its soft water, to reduce estate maintenance costs.
So yes the WHO has a very narrow definition of burn out, but in the absence of any other definition for the above possible factors, I think the populace apply their own definitions and interpretation of burn out, although needing a holiday could be applied to country/location/home burn out whilst not being recognised as burnt out, like I've described above, mainly because to quote Monty Python "Always look on the bright side of life..."
Also, considering the all encompassing nature of the DSM, I'd have thought they would have had some input on burnout, but it looks like they are still contemplating it as a mental disorder.[5]
"Stemming from a lack of conceptual clarity, the current state of burnout research remains, unfortunately, largely circular and riddled with measurement issues."[5]
[1] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2269601/
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3060537/
[3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5635092/
[4] https://pubmed.ncbi.nlm.nih.gov/15080493/
[5] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8945132/