SUMMARY
Searching for multiple file types is not possible at this time. This seems like a basic feature, and it is important, because for large file systems the scanning is the most time consuming part. For example, search for Java and C++ sources at the same time.
Add an option to support standard shell patterns, such as:
*.{java|cpp}

If generic shell patterns are too complicated, at least support an OR operator, such as pipe

STEPS TO REPRODUCE
1. Krusader > Tools > Search
2. Attempt various way to specify multiple patterns at the same time: 
*.{java|cpp}
*.java,*.cpp 
*.java|*.cpp
None work

OBSERVED RESULT
List of files is empty

EXPECTED RESULT
List of files must conform the shell pattern

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
KDE Plasma Version: 5.27.12
KDE Frameworks  Version 5.115.0
Qt Version 5.15.13 (built against 5.15.13)