In document library search
I am missing the "In document library search" which was availlable in the classic experience of the document library.
Another comment says search is still there, but it isn't included on a modern list/library. It includes a filter option, but not search. You have to return to classic view to search.
o365 plan B commented
The search is in there, its located on the top right area. its not as noticeable which I think needs improvement.