[![enter image description here][1]][1]

  [1]: https://i.sstatic.net/jslEX.jpg

It didn't happen to me but happened to someone in our group, I also found a similar post posted a year ago about the same bug but that post didn't have any conclusions as well. (or atleast something that would fix it)

The Similar Post: https://blender.stackexchange.com/questions/248244/header-buttons-missing-please-help

This happened after Blender 4.0 was installed. We checked if some checkboxes are off and re-installed Blender 4.0 as well. Still nothing.

Any help would be appreciated!