I went on to play Minecraft Java Edition a few days ago, and when I tried to place a block, nothing happened. I needed to hold to actually place a block. Now, I tried to heal an iron golem, and nothing, absolutely nothing happened.
*I've only seen this on Minecraft 21w08b (I think), 1.16.5, and OptiFine 1.16.5
Environment
OS: Windows 10, Java Version: Java 15.0
*UPDATE:* Not even holding works today.