I would recommend you don't mix POSIX's strftime, Date::Parse, and DateTime. Since you're already using DateTime, you can use its friends DateTime::Format::Strptime for parsing and DateTime::Format::Human::Duration for output.

use warnings;
use strict;
use DateTime;
use DateTime::Format::Strptime;
use DateTime::Format::Human::Duration;

my $strp = DateTime::Format::Strptime->new(
    pattern => '%m/%d/%Y %H:%M:%S', on_error=>'croak',
    time_zone=>'UTC' );
my $durfmt = DateTime::Format::Human::Duration->new();

my $now = $strp->parse_datetime('01/27/2022 07:40:03');
my @tests = (
        '01/26/2021 07:40:00',
        '03/20/2021 07:40:00',
        '12/20/2021 07:40:00',
        '01/23/2022 07:40:00',
        '01/26/2022 07:40:00',
        '01/27/2022 06:40:00',
        '01/27/2022 07:15:00',
        '01/27/2022 07:39:00',
        '01/27/2022 07:40:03',
        '01/27/2022 07:40:06',
    );

for my $t (@tests) {
    my $seen = $strp->parse_datetime($t);
    print $now->strftime('%m/%d/%Y %H:%M:%S'), " -> ",
         $seen->strftime('%m/%d/%Y %H:%M:%S'), " = ",
        $durfmt->format_duration_between($now, $seen,
            significant_units => 1,
            future => 'in %s',
            past => '%s ago',
            no_time => 'online now',
        ), "\n";
}

__END__

01/27/2022 07:40:03 -> 01/26/2021 07:40:00 = 1 year ago
01/27/2022 07:40:03 -> 03/20/2021 07:40:00 = 10 months ago
01/27/2022 07:40:03 -> 12/20/2021 07:40:00 = 1 month ago
01/27/2022 07:40:03 -> 01/23/2022 07:40:00 = 4 days ago
01/27/2022 07:40:03 -> 01/26/2022 07:40:00 = 1 day ago
01/27/2022 07:40:03 -> 01/27/2022 06:40:00 = 1 hour ago
01/27/2022 07:40:03 -> 01/27/2022 07:15:00 = 25 minutes ago
01/27/2022 07:40:03 -> 01/27/2022 07:39:00 = 1 minute ago
01/27/2022 07:40:03 -> 01/27/2022 07:40:03 = online now
01/27/2022 07:40:03 -> 01/27/2022 07:40:06 = in 3 seconds
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