Help With Armor Texture 2024.4

I'm attempting to make some armor in 2024.4 (1.20.1 Minecraft Version) and all of the infomration online seems out of date. I am particularly having trouble with the armor layer texture. Some say to click the "Create New Armor Texture" button, which doesn't exist. Also whenever I press the "+" next to the "Armor Layer Texture" drop-down menu and select the texture I want, The texture doesn't appear in the drop-down.