Regexp::Common returns regexp objects, so one can drop the outer // and it will compile.

print "P2 has path\n" if ($P2 =~ $RE{delimited}{ -delim => '/' } );
print "P2 has path\n" if ($P2 =~ $RE{delimited}{ -delim => '\/' } );
[download]

Then the escaping becomes a consideration.

use 5.026;
use Regexp::Common qw[ delimited ];

say '\/';
say $RE{delimited}{ -delim => '\/' };
say '\\/';
say $RE{delimited}{ -delim => '\\/' };
say '\\\/';
say $RE{delimited}{ -delim => '\\\/' };
say '\\\\/';
say $RE{delimited}{ -delim => '\\\\/' };
[download]

produces

\/
(?:(?|(?:\\)(?:[^\\]*(?:(?:\\\\)[^\\]*)*)(?:\\)|(?:\/)(?:[^\\\/]*(?:\\
+.[^\\\/]*)*)(?:\/)))
\/
(?:(?|(?:\\)(?:[^\\]*(?:(?:\\\\)[^\\]*)*)(?:\\)|(?:\/)(?:[^\\\/]*(?:\\
+.[^\\\/]*)*)(?:\/)))
\\/
(?:(?|(?:\\)(?:[^\\]*(?:(?:\\\\)[^\\]*)*)(?:\\)|(?:\\)(?:[^\\]*(?:(?:\
+\\\)[^\\]*)*)(?:\\)|(?:\/)(?:[^\\\/]*(?:\\.[^\\\/]*)*)(?:\/)))
\\/
(?:(?|(?:\\)(?:[^\\]*(?:(?:\\\\)[^\\]*)*)(?:\\)|(?:\\)(?:[^\\]*(?:(?:\
+\\\)[^\\]*)*)(?:\\)|(?:\/)(?:[^\\\/]*(?:\\.[^\\\/]*)*)(?:\/)))
[download]

It also appears that Regexp::Common does not de-duplicate the character sequence before it builds the regexp, as the regexps become more complicated as the sequences increase in length.