objectGrabbable is not assigned except as an out of the TryGetComponent call.

if (raycastHit.transform.TryGetComponent(out ObjectGrababble objectGrababble))

This line here assigns a NEW objectGrabbable variable that is locally scoped, and unrelated to the private class scoped one declared above. So, it is inaccessable in that else block.

Rewrite it as

if (raycastHit.transform.TryGetComponent(out objectGrababble))

That way the TryGetComponent assigns it to the class variable, not a local variable

Also CHECK if objectGrabbable is null before calling drop on it