I do have a few blocks that have transluscent and solid parts

Before 1.19, I could merge both models with "loader": "forge:multi-layer"

like that (just an example)

{
	"loader": "forge:multi-layer",
	"layers": {
		"solid": {
			"parent": "modid:block/example_solid_model"
		},
		"translucent": {
			"parent": "modid:block/example_translucent_model"
		}
	}
}

After I updated to 1.19 I received a warning stating "Model loader 'forge:multi-layer' not found" and also displayed the registered loaders

Registered loaders: forge:elements, forge:obj, forge:fluid_container, forge:composite, forge:item-layers, forge:separate_transforms, forge:empty, forge:item_layers, forge:bucket, minecraft:elements, forge:separate-perspective

Does it not work like that anymore? or perhaps the way to do it has changed?

forge 1.19.2-43.0.16

Working perfectly! Thank you!

In case someone else needs it, I also had to change "layers" to "children".