Loaded up 21w05a for the first time, but I didn't get very far before my game became unplayable. After playing for a little while, all of a sudden I couldn't interact with crafting tables/furnaces, blocks could be placed and destroyed but wouldn't drop, mobs wouldn't move and couldn't be pushed or hurt, and I couldn't take damage.
I figured leaving and rejoining the world would sort things out, but when I try to exit, the game gets stuck at the "Saving world" screen. I needed to go to task manager in order to stop it, and when I did, I saw that Java was occupying nearly 2.5 GB of memory and 52% of my CPU. After reopening Minecraft and going back to the world, the problem is still there, and the same thing happens when I try to exit. The Minecraft launcher tells me there was a crash, "Exit Code 0", but there's no crash report file created.