D7 -> D9 module upgrade steps

/* Setting up codebase */
mkdir d7d8mod
cd d7d8mod
ddev config
ddev start
ddev composer create drupal/recommended-project
cp web/sites/default/default.settings.php web/sites/default/settings.php
ddev config
ddev restart
ddev . drush site-install --account-pass=admin

ddev composer require drupal/admin_toolbar
ddev . drush en admin_toolbar_tools

ddev composer require --dev palantirnet/drupal-rector
ddev composer require drupal/drupalmoduleupgrader
ddev composer require drush/drush
ddev composer require mglaman/drupal-check --dev

ddev . drush generate settings-local
// Uncomment conditional include for settings.local.php near bottom of web/sites/default/settings.php

ddev . drush en drupalmoduleupgrader

/* Running Drupal Module Upgrader on the my_drupal7_module module */
// Manually copied D7 version of module in web/modules/custom/
// Analyzed (no changes, just an .html report)
ddev . drush dmu-analyze my_drupal7_module
// Upgraded (converts/adds D8 code, but does not remove D7 code)
ddev . drush dmu-upgrade my_drupal7_module