Fabric 1.20.1
When the Hold Up Animation option is enabled, the held item becomes invisible in third person after a few seconds.
So when viewing another player or yourself in third person, it looks as if the player is holding nothing.

The holdup animation just rotates the arm, it can't hide the held item. Seeing as no one else reported such an issue, I assume you have some incompatible or broken mod installed.

it does not happen when the option is disabled, must be an incompatiblity then yeah
ill look into what mod it might be
thanks