I have now upgraded/migrated the trades persons business listings directory to Drupal 9. I have used very few contributed modules and actually achieved most of the functionality with Drupal core. The only contributed modules I used was to add functionality that is not essential but do add more usability options like users being able to login using Facebook and the Address, geolocation and geocoder modules which make it easier for users to add their business to the map.
Drupal 9 was officially launched 2 days ago (3rd June 2020) so I thought what better way to check it out than to do an actual real life Drupal 9 upgrade. My company website (My Local Trades) was running Drupal 8.8.x and 21 enabled contributed modules.