It’s not a god of gaps argument. It’s a Thermodynamic argument.Our universe had a beginning but that doesn't mean it came from nothing. This is a God-of-the-gaps argument: we don't know what came beforfe the big bang so it must have been God.I don't know how the universe was created so I can't say it was from nothing.
Matter and energy are changing. It cannot stay the same. By inspection it must have a beginning. A beginning that does not violate conservation.
Therefore, matter and energy cannot be eternal without reaching thermal equilibrium. Therefore, the source of existence must be of something not material.
It isn’t possible for matter and energy to exist forever without reaching thermal equilibrium.
So what existed before space and time must have been no thing.