The htop process manager displays
? in the sort command because it interprets the
\t as a tab character, which is not a valid sorting option.
In the sort command,
\t is used as a delimiter to specify the field that the command should sort by. However, in htop, it is not a valid delimiter and is therefore displayed as ? in the sort column.
You can try to use the -k option to specify the sort field and the -t option to specify the delimiter. For example,
htop -u -p -k 2,2 -t ' ' sorts by the 2nd field using a space as a delimiter.
$'\t'sequence but instead just a 1-character tab literal that the shell parsed that sequence into.