It appears that krunner's "document" runner searches the contents of files rather than filenames. Is there a runner that searches filenames instead? Also, when I googled, I couldn't find anything, but is there a wish filed for having an option in the current document runner for searching (only) filenames?

if you're running 4 there is a kio-locate

you should vote for the wishlist

I'm on 5, but I found a bug filed on this: https://bugs.kde.org/show_bug.cgi?id=355767

you can use locate (if installed) in Konsole to search by file name then open with kde-open5 or xdg-open

again you should vote

Unbelievable that this still doesn't work, especially since it worked in kde4!

moreover there is the "image" krunner plugin that indexes by filename, but unfortunately only image files. it should be a simple thing to just copy it and remove the restriction on filenames!