Upgrade to Drupal 9

The upgrade to Drupal 9 was settled at the 14th of November 2021. The complete task is here described:

Install Upgrade Status Modul
Uninstall and remove unused Themes (Bartik, Barrio based Themes)
Upgrade Modules:
    •    backup_migrate
    •    better_exposed_filters
    •    charts
    •    insert_block
    •    libraries
    •    search_api
    •    webform
Remove Module Missing Message Fixer with composer
Remove Patch for insert_block modul

Uninstall and remove Markdown. The Markdown module interferes with insert_view_adv

Create again Text Format „Full HTML“ as it get’s removed when uninstalling the markdown module!!
Move jcarousell to custom and remove from composer

Leave module insert_view_adv untouched

Update module Real name to 2.0.0-beta1
Update modul Single Date Time Picker to 8.x-1.8-beta1
Update modul Webform to 6.1.0
Fix open errors still shown in upgrade status report

Update drupal 8 to Drupal 9 with composer and drush:

chmod 777 web/sites/default
chmod 666 web/sites/default/*settings.php
chmod 666 web/sites/default/*services.yml

composer require 'drupal/core-recommended:^9' 'drupal/core-composer-scaffold:^9' 'drupal/core-project-message:^9' --update-with-dependencies --no-update

composer update

Remove 4 drupal patches from composer.json after update:
https://www.drupal.org/files/issues/2020-11-18/core-8.9.8-references_upgrade_path-2814953-85.patch
https://www.drupal.org/files/issues/2020-09-30/2429699-351--on-8_9_x.do-not-test.patch
https://www.drupal.org/files/issues/2020-07-09/core-ajaxload-1988968-195.patch
https://www.drupal.org/files/issues/2020-09-21/2836054-50.patch

drush updatedb

chmod 755 web/sites/default
chmod 644 web/sites/default/*settings.php
chmod 644 web/sites/default/*services.yml

Reinstall module Missing Message Fixer with composer for Drupal 9

Issues:
Insert Views doesn’t work with leaflet views  => Remove the two views from node 9427 and use blocklayout to place these two views
Check that the SVG images in header and footer still show.