Blessings Darlings!
TL/DR: If it eats and shits, it’s a pet not a familiar spirit.
You KNOW it’s true: damn near every online Pagan group has constant posts of animals and people claiming that the animals/pets are their familiars. Such posts take up a huge amount of bandwidth (I’m so old that I remember when that mattered). So let’s start with what a familiar spirit is and what its traditional functions are.