In Dolphin, the Find File dialog uses wildcard matching for finding files, as in the underlying 'find' command. That's really handy for people who know about wildcards; but it's not intuitively obvious that you have to search for
"*.jpg"
and that searching for
".jpg"
will give no results.
What about making the default behavior be for the Find dialog to automatically include *'s around the search string, so that entering 'foo' will translate behind the scenes to
find . -name '*foo*'
and then include a checkbox to turn wildcards back on?
I started using KDE with about 10 years as a unix user/coder/admin ... for a very long time I was convinced that the Find File dialog in KDE just didn't work, because I wasn't using the wildcards. :)