Yes, I'd vote for folders in Custom slides as well. Have just culled ours from 646 to 582 :)
But what we have done is some naming protocols, grouping all the slides using a overall title for the type of slide it is (such as Greetings, Affirmation, Confession, Collect, Communion, etc) so created an overall section structure which makes it easier to whizz through. I've also used [] (two square brackets) to pull slides like the Lord's Prayer, Grace, etc, to the top of the list. So pseudo foldering until the real folder option appears one day! Similar to AndrewK.
Beware if you pull in old services as templates or repeats as, if you have OLP set to bring in missing custom slides, you'll have to go through and weed them out and put in the revised-named file.
As for AndrewK and what Windows does, if you type your Presentation/Easter 2023 in the search box does it not show all those files for you?