SUMMARY
***
Inside Konqueror, on setting it to be the default application for opening PNG files, new blank windows are spawned until crash. On application restart, Konqueror behaves badly by opening new blank windows until crash. To undo the bad behavior, I remove the lines mentioning PNG in $HOME/.config/mimeapps.list ;;hope this helps in case this bad behavior is present in the latest Konqueror build versions
***


STEPS TO REPRODUCE
1. in Konqueror at address file:///blah/blah/folder
2. select PNG file and adjust settings to make Konqueror the default application for opening PNG files
3. open PNG file

OBSERVED RESULT
Konqueror opens new blank windows continuously until crash.  A new Konqueror session opens new blank windows continuously until crash.

EXPECTED RESULT
Konqueror is the default application for opening PNG file, rendering the image in the new tab after file:///blah/blah/folder

SOFTWARE/OS VERSIONS
Debian 11.2 Linux (aarch64) release 5.10.63-v8+

ADDITIONAL INFORMATION
'''
$ readelf -d /usr/bin/konqueror | fgrep NEED
 0x0000000000000001 (NEEDED)             Shared library: [libkdeinit5_konqueror.so]
 0x0000000000000001 (NEEDED)             Shared library: [libc.so.6]
 0x000000006ffffffe (VERNEED)            0x6b0
 0x000000006fffffff (VERNEEDNUM)         1
'''