How to write an init script that will execute an existing start script in Ubuntu 20.04?

my question similar to: How to write an init script that will execute an existing start script?

However, that question is outdated and I like to know how I can do that in Ubuntu 20.04

This my try in init.d directory:

#! /bin/sh
### BEGIN INIT INFO
# Provides:          myrec
# Required-Start:    $all
# Required-Stop:
# Default-Start:     2 3 4 5
# Default-Stop:
# Short-Description: your description here
### END INIT INFO

PATH=/home/ahmad/recordings
DESC="Recording audio output"
NAME=myrec
DAEMON=/home/ahmad/recordings/myrec.sh
PIDFILE=/var/run/$NAME.pid
SCRIPTNAME=/etc/init.d/$NAME

• I would like to run it after all processes executed, so should I use a systemd service or the above is okay?

• Should I add other code to above or it runs my sh (myrec.sh) file?

In general What is a hello world for executing a simple bash (so that I can see the result) for ubuntu 20.04? Every thing I found in the web is outdated