I’m aware you can select multiple items in the Library to Add to a Collection (hover, select the round dot to select multiple), but that option doesn’t seem to be available when using the Search feature in the Web app. The “dot” isn’t available in the Results displayed. This would be very handy when organizing collections. I have over 500 items in my library so manually scrolling through and selecting them is less than ideal.
That could be a useful feature. In the event it doesn’t get implemented, you can accomplish what you’re looking for using a custom filter in the Library view of your library. You can filter by title (among other things):