The render of the world border follows the player's Y, looking a bit strange.
This may be a side effect from the fix of MC-198864.
A comparison between 20w46a and 20w48a can be seen below.
Linked issues
is duplicated by 5
MC-207869
Worldborder follows players y axis
Resolved
MC-209816
World border following player's Y coordinate
Resolved
MC-213426
World border texture follows the camera instead of being static
Resolved
MC-213596
When you jump in front of the worldborder, then the worldborder animation is jumping with the player.
Resolved
MC-214111
World border follow player Y coord
Resolved
Can confirm.