Starting today, the Drupal 11.x branch is used for building the next major Drupal version, Drupal 11. This means that major version specific changes can now happen on the Drupal 11.x branch. This includes dependency and requirements updates and removal of deprecated API and extensions. Details are available in the allowed changes during Drupal core release cycle document. Drupal 11 is planned to be released either on the week of June 17, week of July 29 or week of December 9, 2024, depending on when beta requirements are completed.
Source: Drupal 11 is now open for development, Drupal 10.3.x is branched