This is on point... You also give no actual numerical context. Are you saying you are working 40 hours a week and leave work exhausted? Are you saying you work 40 at work, and are on call/email/remote terminals for 40 more hours coordinating teams, putting out fires, designing architecture?
Even then, I would ask you to be more specific. I have a normal 40 hour a week uni job as a sysadmin, but it typically takes somewhat more or less (hey, sometimes I can get it done in 35, sometimes its 50 hours). However, for the last several years we have been so shorthanded, faculty wise, that I teach (at a minimum) two senior level computer science classes every semester (I was a professor at another uni). About mid semester, things will break, professors will make unreasonable demands of building out new systems/software/architecture, and I find myself doing (again at a minimum) 80 hours a week. On the other hand, I am not exhausted, as I enjoy teaching quite a bit, and I have been a sysadmin for many years and also enjoy that work.
As you imply towards the end, I think things like numbers of hours worked are generally not relevant for stuff like this. I've been incredibly engaged working 12+ hour days and I've been burnt out barely getting 2-3 hours of real work in a day. It has more to do with the nature of the work.
Even though you only did 2-3 hours of "real work", how much actual time investment was in your job? I don't see how somebody can burn out working just 2-3 hours in a day. Maybe emotionally burnt out if you're a therapist or something, but not as a software engineer.
I guess it was more like that I got burnt out from other things and ended up only being able to get myself to work 2-3 hours.
That said, I wasn't working especially long hours before, either. Maybe not 2-3 hours but still sub-8. The burnout definitely wasn't caused by long hours.
'Burnout' is a pretty ambiguous word IME but in its most commonly used sense it's pretty unrelated to hours worked. My favorite definition is that burnout is a "felt loss of impact and/or control".
Exhaustion/burnout isn't uncommon but without more context it's hard to say if it's a product of the type of work or your specific work environment.