Wow! Looks like just a handful. I sorta imagined you (and several others) would have counts in the thousands. I have 3,751 notebooks and a very rough time finding anything.
I appreciated when @wiltsecarpenter released the notebook on searching within Observable , which helped a lot. Nested collections was also a real enhancement when that came out. But I generally still ache for persistent sort order, a bit more of a UI centered means of searching my collections [again, thanks that we can now achieve this with attributes], and also some means of filtering for time ranges, including differentiating between ‘created’ and ‘modified’ as @bumbeishvili also requests here.