$My::{$symbol} returns a glob.

*NAME{SLOT} accesses a glob's slot.
*BLOCK{SLOT} accesses a glob's slot.
*$NAME{SLOT} accesses a glob's slot.
EXPR->*{SLOT} accesses a glob's slot.^[1]

So,

my $glob = $My::{$symbol};
$glob && *{ $glob }{CODE}
$glob && *$glob{CODE}
$glob && $glob->*{CODE}
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1. Requires Perl 5.24+. Available in Perl 5.20+ by adding both use feature qw( postderef ); and no warnings qw( experimental::postderef );, or by adding use experimental qw( postderef );.