Drupal 9.1 is set to release in December 2020 but will enter the alpha phase this month, Oct 2020 and will have a beta release in November 2020. The minor version update of Drupal will see more deprecations and updating third party packages. However, there are 2 notable changes which will be happening in the Drupal 9.1 release.
A New Default Drupal Theme
Olivero is the new Drupal theme which is in the experimental state. The default theme Bartik has been around since 2011 and has served well over the years. After the Drupal 8 release, a new version of Bartik was released which was responsive out of the box. However, with the change in web design trends, the Bartik theme seems outdated compared to the prowess of Drupal 9 which needed a new modern & clean theme. This is also necessary for evaluators of Drupal to have a good first impression then they assess Drupal for their next big project.
The Olivero theme is added to the Drupal core and will be shipped with Drupal 9.1.0 as an experimental theme. The maintainers are planning to have a stable release and make it the default theme swapping out Bartik in the next minor release - Drupal 9.2
Native Image Lazy Load
One of the biggest factors for a successful website is how performant the site is. Lazy-loading of page elements, especially images, is a powerful way to increase perceived performance, reduce time-to-first-render, and reduce user friction on the web.
The html 'loading' attribute used by Chrome platform which implies to simple add a loading="lazy" to the images to defer loading of the resource until it reaches a calculated distance from the viewport.
This is now added to all images out of the box and will be available in the Drupal 9.1.0 release. Supports any Chromium based browser like Chrome, Edge, Opera, and Firefox (with support for Safari still in progress). This will highly impact the perceived performance of Drupal sites and combined with other mechanisms like Big Pipe, it will greatly improve the performance.
Updated to PHPUnit 9
Another update which Drupal 9.1.0 will receive is for developers. The third-party dependency, PHPUnit which powers solid the testing framework used in Drupal will be updated to the latest version while keeping the support of 8.4 for backward compatibility. This update was added to make Drupal 9 ready for PHP 8 which will be releasing on November 26th, 2020.
Other changes which are included are mostly deprecation of methods and introducing overridable services. A full list of change records can be found here.