Quora seems to create a random ID for the header each page refresh. Mine currently is
###__w2_aBrjao6_header. The consistent parts are
__w2_ is used in other elements, sadly.
So you can select the
_header part and have uBlock Origin block that using the following (CSS) selectors:
##[id *= "_header"] /* Contains */
/* OR */
##[id $= "_header"] /* Ends in */
/* ... */ parts are just comments, don't include them when selecting elements in uBlock.
It seems that the first two
## are used by uBlock Origin as an identifier. We don't want the third because we aren't technically selecting a specific ID, we're selecting a type (but in reality that there is only one matching element per page).
The easiest way to add the rule is to start uBlock Origin on the page, select something with it's ink-dropper tool ("element picker mode"), then change the rule to one from above.