\&{$x} works perfectly fine with strict refs. It is only implicit usage of strings as references that is prohibted by strict refs. If you go to the length of writing \&{ ... }, perl assumes a symbolic reference is indeed what you want.

use strict;
use warnings;
use 5.010;

sub Foo { 'in sub Foo' }

my $x = 'Foo';

my $sub_ref = \&{$x};
say $sub_ref->();
__END__
in sub Foo
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