Major operating system updates are tricky and often cause compatibility issues, which is what many Raspberry Pi users unfortunately experienced after updating the popular single-board computer to the latest OS version, which is also known under the name "Bullseye". This Raspberry Pi OS update brought many improvements like a free performance boost, but at the same time caused serious head aches for some users.
The aforementioned OS update apparently made the Raspberry Pi (from US$53 on Amazon) incompatible with certain HAT interfaces, video drivers and camera modules. In order to resolve these issues, the company has now released the Raspberry Pi Legacy OS, which utilizes the previous Debian version also known as "Buster". This downgrade also means that Legacy OS cannot offer certain features like the new hardware acceleration for Chromium based browsers, which will now be reverted back to software-based acceleration.
However, the Raspberry Pi Legacy OS is also based on the older Linux kernel 5.10, which means that it should once again be compatible with older drivers and interfaces. This additional Legacy OS version for the Raspberry Pi will be adequately maintained and receive security patches and updates in the future. All further technical details on the new/old OS for the Raspberry Pi are discussed in the according official blog post, which also includes download links to the Legacy OS for the Raspberry Pi.