set -o emacs ; stty -echo

[Andrew Cagney <andrew.cagney%gmail.com@localhost>]

should, like for bash, this put the terminal into -echo mode?

arm64$ echo $SHELL
/bin/sh
arm64$ set -o emacs ; stty -echo
arm64$ pwd
/home/cagney

other combinations are equally puzzling.  for instance:

set -o emacs ; stty -echo ; set +o emacs
doesn't flip to -echo mode either