Vanilla refers to Minecraft as a standalone game, without mods or addons.
Vanilla can also refer to spices derived from the orchids of the genus Vanilla, primarily obtained from pods of the Mexican species, flat-leaved vanilla.
<----------vanilla
So in the latest beta version of Forge (1.16.1) when you install the latest version of Optifine (1.16.1) and apply a shader, any items that you have will have no texture and will be invisible. Although the items themselves are invisible, the tooltips for the items and the stack number are still visible. I do not know if this is an issue with Forge or with Optifine though. Even using the internal shaders will produce this effect.
To recreate:
Optifine Link: [removed link to illegal third party site - diesieben07]
Forge Link: http://files.minecraftforge.net/maven/net/minecraftforge/forge/index_1.16.1.html