grep -P xxx file.txt

"The -P option is not supported"
Removed from the manual page via this commit.

PR:	99831

gnu/usr.bin/grep/grep.1

@@ -202,11 +202,6 @@ Interpret
 as a list of fixed strings, separated by newlines,
 any of which is to be matched.
 .TP
-.BR \-P ", " \-\^\-perl-regexp
-Interpret
-.I PATTERN
-as a Perl regular expression.
-.TP
 .BI \-f " FILE" "\fR,\fP \-\^\-file=" FILE
 Obtain patterns from
 .IR FILE ,