SUMMARY
Turning off bookmarks in the krunner settings has no effect.

STEPS TO REPRODUCE
1. In the krunner settings, turn off the checkbox for bookmarks 
2. Search for a string matching a bookmark

OBSERVED RESULT
Bookmarks are shown.

EXPECTED RESULT
Bookmarks are not shown and most importantly also *not searched*

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.19.4
KDE Frameworks Version: 5.73.0
Qt Version: 5.15.0
Kernel Version: 5.8.3-arch1-1
OS Type: 64-bit
Processors: 24 × AMD Ryzen 9 3900X 12-Core Processor
Memory: 15.6 GiB of RAM
Graphics Processor: GeForce RTX 2080 SUPER/PCIe/SSE2

ADDITIONAL INFORMATION
Background, i tried to turn of bookmarks search because of a bug in the bookmarks search that causes excessive disk writes. This means that currently all krunner searches cause excessive disk writes and there is no way to avoid this bug except for not using krunner at all.
https://bugs.kde.org/show_bug.cgi?id=417070