Free will exists and is fully compatible with determinism. The whole issue is a pseudo-problem born of an incoherent understanding of modality.
I'd be interested to hear some elaboration on this.
Free will, in the sense that actually matters to discussions of human agency, is the idea that a person's actions are a product of their own conscious choices. We sometimes act in ways that weren't dictated by our free will, to the extent that a lot of our behaviors are driven by instincts (I don't really choose to pull my hand away from a hot stove). But obviously we also have plenty of latitude for conscious choices as well, or else the distinction wouldn't even make sense in the first place.
Under this framework, whether the universe is deterministic or not has no bearing on the existence of free will. My choices don't become less free or less genuine by virtue of being part of a larger causal chain. Indeed, as Alcibiades points out, it would probably be more damaging to our common sense of free will if indeterminism is true, since it would mean our decisions are ultimately random and thus in some sense meaningless. I don't think that means free will wouldn't still be a thing in such an universe (I think the existence of free will is a self-evident truth) but either way, I'd rather live in a deterministic one. Viewing our own choices as parts of a causal picture allow us greater control over them, and thus ultimately greater freedom to act according to our more fundamental values and preferences. If I know putting myself in a certain situation will lead me to make choices I come to regret, I can do a better job avoiding that situation and thus have more agency over my own life.
The problem with discussions of free will is that they tend to be riddled with ambiguous if not outright incoherent understandings of what we're even talking about. A concept that's often bandied about is "the ability to have done otherwise". Now, to me, it's pretty obvious that I do have the ability to do otherwise. Instead of typing at my computer right now, I could pick it up and throw it out the window. There is no force external to me that's preventing me from doing that. But I don't want to do it, and I have specific reasons for not wanting to do it. These reasons, taken together, determine my choice not to throw my computer out the window, but they don't take away my ability to do so. For some reason, proponents of libertarian free will disagree with this - they think I'm not truly free to throw my computer out the window if I have deterministic reasons not to want to do it.
The root of the problem, to the extent I understand it, seems to be that "the ability to have done otherwise" is construed as a metaphysical concept. That's where we get to the problem of modal logic. For some bizarre reason a lot of philosophers seem drawn to the idea that modal concepts (possibility, necessity, impossibility and contingency) are fundamental metaphysical entities. I never understood the appeal of these views, as I always saw these concepts as being easily reducible to easier-to-grasp concepts of uncertainty and counterfactuality. They also lead to some embarrassingly bad lines of thinking, such as Gödel's attempt to resurrect the beaten-down corpse of the Ontological argument (I'm sure you'll get a kick out of that given your religious views).
Anyway, if you take possibility to be a fundamental metaphysical category, then "the ability to have done otherwise" seems to mean not only that you're physically capable of another course of action, but that you're capable of wanting it irrespective of all the reasons you might have not to want it. So I'm only free to throw my computer out the window if there exists a possible world where all the other facts are the same but somehow I did in fact throw my computer out the window. To me, this is patently ridiculous. We'd have to imagine that somehow all "free" beings are prime movers, even though all evidence points to us being as subject to the laws of causality as everything else in the universe. I guess a lot of people feel like the kind of free will I subscribe to is not true free will? To me, it's the only definition of free will that makes any sense, and libertarian free will advocates are only making hard determinism more plausible by holding to an impossible standard.