Thanks! So, in order to allow my method of processing command line options to continue to work while using the v5.36 features, I can write:

use v5.36;
use feature qw/switch/;
no warnings "experimental::smartmatch"; 
no warnings "experimental::for_list";

for my ( $opt, $val ) (%$opts ) {
    given ($opt) {
        when ('h') { HELP_MESSAGE(); }
        when ('v') { ++$verbose; }
        when ('r') { ++$recursive; }
        when ('c') { ++$confirm; }
        when ('f') { ++$force; }
        default    { die "*** BUG: no handler for -$opt.\n"; }
    }
}
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To me, this reads the best. I guess that if given goes away I'll replace it with for .. reluctantly, because "for" has always implied looping to me.