Sounds like an oxymoron, right?
God is central to Judaism and you can’t write them out of it. But the question of the nature of God is not really an important one in Jewish traditional theology; we’re not preoccupied with God, we just accept that God exists and don’t worry about it too much.
The existence of God is this assumption that you have to make to get it all to work rhetorically, but the reason it works in practice is because Judaism, at its core, is materialist and humanist.
Jewish socialists were such a force before the Holocaust, because a kind of socialism is already embedded in our tradition; you just have to know how to look for it. What the Sages created is a path to establish a utopian, essentially communist society that is able to survive inside the existing, oppressive and exploitative societies; a way that can slowly transform the world by making tiny revolutions, one action at a time. That’s what the Mitsvos are: the result of an ongoing, 2,000+ year old conversation on how exactly to create a materially just society that works.
This is why I think that the value of Judaism for socialists is to deeply engage with tradition, rather than to replace it with a secular religion or water it down to make it more consumable, or to adapt it to the shitty world we live in. The world should adapt to the Law, not the other way around. The Mitsvos are binding because the world can only be changed through material action, and because we all have to act together.