As of 21w06a, there is tremendous FPS lag. I am averaging below 20 fps when previously rarely see below 100 fps. There are not really lag spikes, it is more just general lag. And it isn't chunk loading lag, as they seem to load almost normally for me, it is just rendering FPS lag.
This occurred when I was spectating the caves underground in spectator mode, though I would assume it would occur with any game mode.
I'm fairly certain this is caused by the new world generation in one way or another.
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This is normal. This should be optimized in the next versions of the game

Thank you for your report!
We're tracking this issue in MC-214898, so this ticket is being resolved and linked as a duplicate.
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Mods, please reopen.
This is not the same bug. MC-214898 specifically regards chunks loading slowly and does not mention framerate; this involves the game being choppy and chunks behaving normally.
The reporter of the bug MC-214898 specifically commented that their FPS was fine for them. (It must be somewhat dependent on environment.)
This is actually a duplicate of MC-214883

Ok thank you, at least I know it was reported and my issue isn't closed because of the wrong bug. This is at least the third time my duplicates have been resolved as the wrong issue, even though I've provided a detailed description.

@@unknown, as commented on MC-214883 by @unknown could you please provide screenshots or videos showing a comparison between the versions (ideally under the same circumstances to make sure the results are comparable)?
Might be because of the increased world height and depth