Win8 Strawberry 5.8.9.5 (32)  Fri 01/15/2021 18:04:55
C:\@Work\Perl\monks
>perl -Mstrict -Mwarnings -MData::Dump=dd

my $s = q(AAAAbbbbCCCCddddXeeeeeeeeeeX);

my @caps = $s =~ m{ (?<! \A .{16}) \G .{4} | .* }xmsg;
dd \@caps;

^Z
["AAAA", "bbbb", "CCCC", "dddd", "XeeeeeeeeeeX", ""]