Cut and paste this URL to share the unmodified register and value:
https://regviz.com/r/STMicroelectronics/STM32U599/GFXMMU/GFXMMU_LUT15H#0x0
GFXMMU LUT entry 15 high
Line offset Line offset of line number x (i.e. offset of block 0 of line x)
https://github.com/cmsis-svd/cmsis-svd-data