All morals are subjective
You are conceptualizing and reifying patterns of reality here, and you need to first understand what morality is, and what objectivity is, and what a "proof" would mean before you even begin speaking these words. I'm not saying that you don't have some internal understanding of the meaning, but it's likely a generic dictionary meaning as opposed to how that meaning maps to reality.
From a ground of certain philosophical presuppositions.
a) Reality is objective
b) Our perception of reality is subjective.
Hence, you end up switching these categories when we are discussing morality. We generally presuppose, and hopefully agree, that if we close our eyes then the world out there doesn't stop functioning. Right?
We can also agree that our perception allows us to merely detect "reduced patterns" that we derive from our senses. These patterns end up mapping to other patterns, and that's how we derive a "model of reality" that our brains use as operation map.
That's essentially what knowledge is. It's a model of reality that exists as interlinking network of concepts that we rely on to map reality and figure out what we see, and what to do with what we see.
I hope we have some agreement on that so far.
What we call morality is not much different from any given "proper contextual behavior" that exists in our brain, except that it takes into account a broader range of our "shared patterns of behavior" that we communicate to each other and compare.
Thus, morality IS NOT subjective in a sense that there are limited amount of behavior that doesn't lead to your death, or death of your kind. You can't say that you subjectively decide not to jump from the roof of the building, because there is a very good objective context out there.
unless you can demonstrate PROOF that not only God exists, but that God's dictates are actually objective.
It doesn't work like that in context of what God is. God, from our position of reality of "here and now" is a foundational presuppostion... and it can only exist as a foundational presupposition.
In short, God is an axiom derived through certain necessity for having a coherent model of reality. It's not something that you "prove". It's something that you presuppose to use as a foundation in which certain context of proof can be possible.
You make plenty of foundational assumptions that you can't prove. Hence, I don't generally demand you to prove them before you can have grounds for some moral proclamations.
God axiom at its core, if we strip any other presuppositional dogma assumes that there's a guiding force that arranged our reality as certain way, as opposed to having an arbitrary reality in which meaning WOULD BE subjective and preferential.
Hence, it's actually a presupposition out of certain necessity to have meaning as opposed to having arbitrary consensus.