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.
Many of these incompatible modules have been posted by people who contributed their code but don't have the capacity to maintain it. I don't think that is a problem. That they contributed in the first place, and that their contribution is so useful that it is used on live Drupal sites itself proves the value. So I think we should appreciate and celebrate these folks. On the other hand, we need to acknowledge the lack of maintenance and find new maintainers who can bring these projects forward.
There is an existing process for taking over abandoned projects on drupal.org, however the Drupal Association decided to speed up the first steps of this by automatically opening issues in the affected project's queues two weeks before DrupalCon Europe. You can find the over 3 thousand projects that are under this process at https://bit.ly/drupaladopt (open issues tagged with "Project available for adoption"). If an issue has already been closed, that means the maintainer has declined new maintainer help, so please look at the open issues only.
The steps to request co-maintainership are:
Comment on the issue explaining why you would like to maintain the module.
If the project is opted in to security coverage, confirm that you have previously received security coverage opt-in permission.
If an existing maintainer has not commented, move the issue to the Drupal.org Project Ownership queue by editing the 'Project' field on this issue.
From there, a Drupal.org Site Moderator will review the issue and grant maintainership if the requirements are met.
Once you gain co-maintainership, make sure to commit the Drupal 9 compatibility fixes and make a release of the project, so people can rely on a fixed codebase for their sites.
You rock! Thanks for keeping a part of Drupal's ecosystem up to date!