Well in my personal opinion, there's extremely few material goals that have any purpose whatsoever, life is short, matter is ephermal.
Usually, I find, one has to invest an enormous effort to just find that purpose in the first place. And trying out paths/goals is part of that journey too.
I know I did a lot of soulsearching, in fact I was privilledged enough to save up for a couple of years to do JUST that, and I can report that it was a resounding success (with a sample size of one!).
However, as we're discussing this in the context of burnout, it's obvious that having a higher meaning did not take me out of my suffering. I still experience life as any other human being, I just feel like my life is not wasted - and the side effects of always striving for a goal - like focus and discipline - and other virtues - are a pleasant bonus. So I do sincerely think, that having a crystalized idea of my purpose creates a happy life for me.
There's nothing wrong with NOT having a goal, I just couldn't do it, even though matter IS ephermal, I believe that every action that we take, ultimately does have meaning.
> even meaningful work becomes mundane once your brain adjusts to it.
Not to demean your experience, but for me (5+ years now of daily grind for one purpose) that statement is very VERY real.
My thinking is - it's just another one of the struggles of doing real meaningful change - there's recurring, long and arduous timespans where no observable/exciting results manifest and one has to trudge forward.
If you know how to ease THAT part, please share (I'm begging you lol).