NecrochildK

Nevermind. Optifine's absolute newest version fixes this. For anyone having this issue, Optifine 1.16.1 HD U G2 Pre9 is compatible again with Forge.

Additionally, this only happens when using Optifine within Forge. Optifine does not cause this with versions 32.0.43 and below

In 32.0.44 and above, all inventory items are invisible and when held in hand or dropped, the item looks scrambled. Spent all night narrowing it down to find which version this issue started with. Image is a full item bar, stack of sand in first slot and hand and the weird squiggles are all sand blocks dropped.