Whilst working on a plugin I noticed that the

Player#setWalkSpeed

method was not working.
This previously worked fine in 1.15.2, when setting it in 1.16.1, the player's field of view changes (albeit it appears to be backwards) but the actual movement speed does not change at all.

Simple Test:

player.setWalkSpeed(0.5f);

Expected: This value should speed the player up.

Result: The field of view "zooms in" as if the player were to slow down. Their actual movement speed does not change.

player.setWalkSpeed(0.01f);

Expected: This value should slow the player down.

Result: The field of view "zooms out" as if the player were going to be moving very fast. Their actual movement speed does not change.

Have I tested on vanilla:
No I have not, Im not entire sure if/how I would be able to modify a player's speed in vanilla.
This could potentially be a vanilla issue, I'm not quite sure.

Including a plugin:
Yes, I have included a simple plugin to test speed.

/test [speed = float]

You can choose your speed here, ex:

/test 0.5
or
/test 0.01

or you can simply negate the float and it will reset back to default 0.2f