You need to enable file indexing, some GNU/Linux distributions disable it.
That’s in systemsettings > Search > File search.
Then first checkbox, enable.
You can include or exclude specific folders like ~/Desktop you don’t want to index.
The file indexer (baloo) will then read all the files in the folders specified, extract information about them (names, dates, meta-info like image height and width, etc) and store them in a database.
This data is then available in dolphin.
Indexing takes time, your files might not be already index, if you have your HOME it it will read every file in there, and potentially all of their content since you checked (“Also index file content”)
how do i get it to work on existing files?
It does not make a difference.
do need both of those boxes checked?
do i need to add each individual folder, or does it do recursion, and if so why didn’t the original home folder take care of it?
It is recursive.
You can check how many files were indexed with balooctl status.
If that still does not show in dolphin, that’s a regression.