GPU usage (viewed from Task Manager) shoots up to 60% on the title screen, causing it to lag. Going into any menu stops the high GPU usage (drops down to 3%).
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Can also confirm, especially when maximized.

Confirmed for me too, I get about 10 fps.

It's very lag at Title screen, background animation moves tick by tick

Oddly enough, the title screen runs really smoothly for me.

100% GPU usage for me. Maximizing the Minecraft window causes frame rate to drop. Tried lowering the resolution of the new panorama via resource pack, and it does not work.

still present in 1.17, but not to the same extent
the game also tends to cause huge system-wide stutters on certain hardware when starting up
Can confirm. The title screen is very laggy for me as well.