https://perldoc.perl.org/perlref#Declaring-a-Reference-to-a-Variable

Beginning in v5.26.0, the referencing operator can come after my, state, our, or local. This syntax must be enabled with use feature 'declared_refs' . It is experimental, and will warn by default unless no warnings experimental::refaliasing is in effect.

In reality is the warning disabled with no warnings 'experimental::declared_refs';

the experimental::refaliasing warning belongs to https://perldoc.perl.org/perlref#Assigning-to-References

Sample code:

use strict;
use warnings;
use Data::Dump qw/pp dd/;

use feature qw(
        declared_refs
        refaliasing
        say
   );



no warnings 'experimental::refaliasing';
my $a = [666];
my @a;
\@a = $a;

say $a[0];


no warnings 'experimental::declared_refs';
my \@arr = [42];
[download]

C:/Strawberry/perl/bin\perl.exe -w d:/tmp/pm/auto_ref.pl 
666

Compilation finished at Sat Oct 16 14:45:33
[download]

NB: that use feature qw(declared_refs) doesn't seem to make sense without the other feature.

my \@arr; without assignment will create a new warning "Useless use of single ref constructor in void context"