wc.p6

use v6;

sub MAIN (:$sep = "\t", :$min = 0) {

    my ($lines, $words, $chars) = 0 xx 3;
    
    for lines() -> $l {
	$lines += 1;
	$chars += $l.chars + 1;
	$words += $l.subst(/<-alpha -space>/,'',:g).words.grep(*.chars >= $min);
    }
    
    say ($lines, $words, $chars).join($sep);
}

Try this:

sub MAIN (*@files, :$sep = "\t", :$min = 0) {
    @*ARGS = @files;

    # ....rest as before
}

Or more concisely, at the risk of confusing readers:

sub MAIN (*@*ARGS, :$sep = "\t", :$min = 0) {
    # ....rest as before
}