SUMMARY
Dolphin cannot operate on files whose names contain non-UTF-8 bytes
(e.g. Windows-1251); the filename is shown as question marks and any
operation fails with "The file or folder XXX does not exist".

STEPS TO REPRODUCE
1. Open Dolphin and go to any writable directory.
2. In a terminal in this directory, create a file with a non-UTF-8 name, e.g.:
  
   touch ''$'\312.txt'
  
3. In Dolphin, try to rename, delete, or perform any other file operation
   on the created file.

OBSERVED RESULT
- Dolphin displays the filename as a sequence of question marks instead of
  the actual characters.
- Renaming, deleting, or performing other operations on this file from
  Dolphin fails with an error dialog:
  "The file or folder XXX does not exist".
- The file remains in the directory, but it cannot be manipulated from
  Dolphin’s UI.

EXPECTED RESULT
- Dolphin should be able to operate on such files (rename, delete, move,
  etc.), even if their names contain invalid or non-UTF-8 byte sequences.
- At minimum, Dolphin should not report that the file "does not exist"
  when it is actually present on disk.

SOFTWARE/OS VERSIONS
Operating System: Arch Linux 
KDE Plasma Version: 6.5.3
KDE Frameworks Version: 6.20.0
Qt Version: 6.10.1