While a lot of Drupal extensions are now compatible with Drupal 9, it can happen that you encounter an incompatible extension. In case adopting the extension fits into your plans, that is the best way forward. However, there may be some delay until you can adopt the project and it may not fit into your plans to adopt in the first place. There are a few solutions to use drupal.org projects that are distributed as incompatible on your Drupal 9 sites.
Various people in the Upgrade Status issue queue are concerned about the module requiring Composer though. While Drupal 8 or 9 do not require Composer to work, getting any extension installed on your site that depends on third party components is a sizeable challenge without Composer. With Drupal 8 core dependent on various third party components, it was inevitable that a dependency manager will be needed to build Drupal sites. Upgrade Status itself does require various third party components to check for deprecated API uses and even to locate your Drupal site root. So you cannot avoid using Composer to even check for Drupal 9 compatibility.
With eight days to go until Drupal 8's end of life (on November 2, 2021), now is a good time to take stock of your Drupal 8 sites' modules. Use Upgrade Status to check for environment and module compatibility with Drupal 9. While more than 7 thousand modules are now Drupal 9 compatible, there are still various that are not yet compatible. However, most only need a one line change and a release or even if they need more, an automated fix is posted to their issue queue and is tested by the community.
With the Drupal 8 end of life in a little over two months and Drupal 10's release next year, this is the time of transitions again at Drupal. However, while Drupal 7 to 8 (or 9) was a big move, the transitions from 8 to 9 and 9 to 10 are much smaller and mostly automated.
Drupal 10 is planned to be released in June, August or December 2022 and the tools are getting ready to support that. The two key tools will be the same as the previous upgrade: Upgrade Status and Drupal Rector.
Matt Glaman has been doing amazing work recently in the underlying components of both tools. Thanks to his work on updating phpstan-drupal for Drupal 10 support, Upgrade Status checks deprecated API uses on Drupal 9 too. Since my last update on that, I added reporting of deprecated modules and new system requirements as well.
How is this different from prior releases of Upgrade Status? It should run very similar on Drupal 8 as it did before. However prior releases of Upgrade Status explicitly forbid running it on Drupal 9 as the UI was very focused on the transition from 8 to 9. Now the UI elements are adapted and in some cases more general to support running either on Drupal 8 or 9.
Do you own an existing drupal.org project that does not yet have a Drupal 9 compatible release? This week would be a good time to take that step and make a Drupal 9 compatible release! I am paying for two tickets to DrupalCon Europe for new Drupal 9 compatible releases. Read on for exact rules!
DrupalCons are a great way to learn and connect, but they are especially great to meet various people leading Drupal's future direction. DrupalCon Europe in a couple weeks is no exception.
The initiative leads provide a glimpse into their respective areas in the Drupal Initiative leaders keynote. This is a great way to get to know the leaders and learn more about their plans and where you could help.
Various initiatives have dedicated sessions as well.