Im in 1.19.4 minecraft trying to build a mapart using litematica version 0.14.3 and malibib 0.15.2 but when I open up the Material list for schematics, none of the materials are there.

Is it a large schematic, does it go outside of your render distance? Then you need to move around to load the chunks shown on the bottom right HUD, if you use the placement-based material list that has to count the blocks from the world.

If you don't need the current progress or render layer limited material list, but you just want the total materials for the entire schematic, then you can open the material list directly for the schematic file from the Load Schematics menu.