Drupal is a free, open-source, flexible, and secure content-management framework for website development. 
It handles large and complex websites very well. 

Drupal has been found to have a lower approval rating among new users compared to expert users. 
This led to an initiative being launched by Drupal's founder, Dries Buytaert, to address the needs of beginner users. 

On the surface, this doesn't make sense. Any average D10 site is probably one of the most complex #symfony apps in the world. When Drupal 8 was being built, I remember how the community found and patched a ton of edge case bugs in PHP and Symfony because it is SO BIG and so complex.

Drupal 10 will be supported until the release of Drupal 12 in mid-late 2026
Beginning with Drupal 10, a new Drupal major version will be released every two years in even years (2022, 2024, etc.). 

The fifth and final feature release of Drupal 9 brings a stable CKEditor 5 module, a command line theme generator, and helps prepare for your update to Drupal 10. 
Bugfixes will be provided for Drupal 9.5 until June 2023 and security fixes will be provided until November 2023.

In Drupal 10.1, completely rewritten aggregation generation logic solves both of these issues.

Aggregates are now built by a dedicated route, with the main request only responsible for generating the aggregate URL based on libraries, theme, language, and grouping logic.

A comprehensive idea of who, and why they are visiting your site, as well as a common language for stakeholders to use,
means we can more easily define complex functionality.

As we develop a set of scenarios, the team ensures that all of the desired functionality is represented.

Drupal 10 - New Features, Release Date, Migration/Upgrade

Drupal 10 will be a refined version of Drupal 9 including all the goodies from all initiatives. It will include Olivero, Claro, all the work from the Automated Updates Initiative, Bug Smash, Easy Out-of-the-box, Decoupled Menus, and the Project Browser if we have one in time.