In the 'U599/'U59A, 'U5F7/'U5G7 and 'H7Rx/'H7Sx families, there is a new graphics module, called Neo-Chrom or GPU2D. According to ST's description:

The GPU2D is a dedicated graphics processing unit accelerating numerous 2.5D graphics applications such as graphical user interface (GUI), menu display or animations. It works together with an optimized software stack designed for state of the art graphic rendering.

This graphic processor is, and remains to be, undocumented.

ST's position (as conveyed by user GaetanGodard) is:

The NeoChrom GPU documentation will not be made public.
ST partners providing GUI libs supporting STM32 with NeoChrom GPU have access and have already, or are working on, utilizing NeoChrom GPU capabilities to its full extend.

So, as of now, it appears, that this module is entirely useless to those who don't plan on using some of the software bundles which support it (probably TouchGFX).