Versions ars_nouveau-1.19.2-3.4.2.jar and geckolib-forge-1.19-3.1.24.jar are incompartible. Some textures disappears for example magic blocks and archmage book.

Version geckolib-forge-1.19-3.1.25.jar does not lost textures but loses color of coljured mage blocks: they are RGB 1-120-1 (grass-green) but looks like gray.

Also experiencing this with geckolib on 1.18 geckolib-forge-1.18-3.0.45 and geckolib-forge-1.18-3.0.41

This has been fixed in geckolib 1.18-3.0.45 (and latest 1.19), are you sure you are still experiencing this issue? Should be fixed now.

Yes, just fixed in geckolib-forge-1.19-3.1.27.jar