Just yesterday my game was running fine in 20w21a with 50 FPS. When I logged on today on the same world, in 20w22a and I was running 7-8 fps. I do have a older graphic card, And I saw that minecraft said they added experimental changes in rendering the may effect a small amount of older graphic cards.
Environment
Java Version of minecraft
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However, this issue is a Duplicate of MC-186075.
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