ok, I've got a new character that's a Bard. Using Additional Magical Secrets it has the spell Find steed ( usually a paladin spell) and Ability Score Improvement giving me the spell find Familiar, the find steed says you can have only one steed and find familiar says you can only have one familiar at a time, but neither spell makes reference to the other, so my question is, would summoning a steed or a familiar, banish the other one ? or is it a DM decision?

Familiar and steed are separate entities and neither spell says that it gets rid of the other, so you can have both at the same time.