The creaking mob was initially revealed and released in 24w40a with an emissive eye texture that would glow in the dark without emitting light, similar to spiders, endermen, as well as several other mobs.

Creaking in version 24w40a.

With the current snapshot release and the experimental pack included with 1.21.3, this is no longer the case. This is especially noticable when they are placed next to the new eye blossom flowers.

Creaking in version 24w44a.

Creaking in the experimental pack for 1.20.3.