SUMMARY
When a file name contains special characters (ie. newline), they are not visible in the displayed name.

STEPS TO REPRODUCE
Using Python to avoid any bizarre things with how shells interpret special characters in the input :
1. os.chdir("/tmp")
2. open("test\ntest", "w")
3. open("testtest", "w")
4. open("test\rtest", "w")
5. Show /tmp in dolphin

OBSERVED RESULT
Three files that appear as testtest ; only by using the renaming tool does the newline appear (but the \n and \r remain indistinguishable).

EXPECTED RESULT
Some visual clue that the filename contains a newline character.

SOFTWARE/OS VERSIONS
KDE Plasma Version: 5.18.5
KDE Frameworks Version: 5.68.0
Qt Version: 5.12.8

ADDITIONAL INFORMATION
This might be used to craft a file mimicking another file.

Inserting a tabulation gives a clue (the tabulation is displayed).
Inserting other special characters (eg. ASCII 1 or 2) gives a small black box with the character mnemonic.