SUMMARY
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The file name patterns and mime types to be excluded can only be configured in ~/.config/baloofilerc and not via the graphical interface in file search settings.
This makes this setting hard to even find, and some users might feel uncomfortable editing dotfiles.  
In addition, a graphical interface with a list of file extension and mime types to select from would make it easier to come up with the right elements to put to e.g. exclude all image file types from indexing, rather than having to find and enter all applicable mime types or file endings by hand.
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STEPS TO REPRODUCE
1. System Settings > Search > Flie Search

OBSERVED RESULT
No option to configure file patterns and mime types to exclude from indexing. Have to go edit ~/.config/baloofilerc.

EXPECTED RESULT
Graphical configuration for file patterns and mime types to be indexed.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux
KDE Plasma Version: 5.24.4
KDE Frameworks Version: 5.93.0
Qt Version: 5.15.3
Kernel Version: 5.17.4-arch1-1 (64-bit)