@Golden Helmet: It's possible, but this issue is consistent and only began with 1.20.10. It NEVER occurred on any of the realms I've played on prior to 1.20.10. And once it did happen, I tested it multiple times just to be sure it wasn't a one-off or two-off issue. It happens every time now, and never did before.
I can confirm that this is happening with CavesAndCliffsPreview datapack. It does not appear to happen when that datapack is not loaded.
You can see the lag spikes in my screenshot, I was walking back and forth across a chunk border.
As soon as 1.20.10 dropped, I have had similar issues with the Wither. I spawn the wither over an ocean to prevent block damage. Since 1.20.10, as soon as the Wither gets to phase 2 (glows, shakes, explodes, drops wither skeletons), it shoots straight down up to 60 blocks in some cases in a perfect 8x8 column. This behavior is replicable and new to 1.20.10.