Adobe will stop supporting Adobe Commerce versions 2.3.x in precisely two weeks. The 8th of September is the last date for quality and security fixes for all the lines' releases starting from 2.3.0 to 2.3.7.
Initially, the date was scheduled for March this year, but it was postponed. The date change likely happened because of the planned release of Adobe Commerce 2.4.4, which contains a wide variety of improvements, including support of PHP 8.1, which became available in November 2021, so the developers needed more time to prepare the new version of the e-commerce platform.
The 2.3.x release line was in active development for quite a long time - starting from 2.3.0, which became available on the 28th of November 2018, until 2.3.7, which was released on the 11th of May 2021 and received the last patch (2.3.7-p4) about two weeks ago, on the 9th of August 2022.
Once the release line reaches the end of support, updating the platform to the latest version is recommended to avoid possible security vulnerabilities that might be discovered later. It won’t be patched and get the new features. In the latest releases, Adobe worked to make platform maintenance easier. However, migration may be complex if you’re using a heavily customized version of the platform (including third-party extensions).
Also, it is worth mentioning that there won’t be a single end-of-support date for the release line 2.4.x. Instead, it was split into a few parts. Currently known are 2.4.0-2.4.3 (end of support scheduled for the 28th of November, 2022) and 2.4.4-2.4.6 (end of support scheduled for the 25th of November, 2024).