> I can't think of a program that isn't an IDE that has taken this approach, though.

There aren't many, but on the other side... IDE developers are dog-fooding their product. They want customizability, they know other developers will want that customizability, and they get their wishes granted.

The JAWS screen reader for Windows has had a searchable settings UI for several years. I regret that I and possibly my coworkers, working on a competing product (before I went to Microsoft), used to privately mock that search feature, taking it as evidence that JAWS had gone overboard with settings.

KDE settings also has settings search (also windows more or less and other comment mentions mac). An OS is not a program but...close.

VLC

Emacs. You can search for all settings. And completely replace them.

Firefox on desktop?

JetBrains products have searchable settings