Classical free will, going back to Hobbes, is really just that sometimes we act unencumbered by external forces. Determinism posits that no one can act other than how one ultimately does.
Those could be compatible.
There is a difference between me deciding to stay in a room after careful deliberation, and me being chained to a wall in that room in spite of my protest.
Even if the future is fixed, there's still a difference between a person being forced to do something by an external actor and a person doing something they would ordinarily do.
Modern neuroscience wouldn't tell you very much that's useful about external forces.
All Hobbesian free will is committed to is that being chained to a wall changes your circumstances. Being kidnapped deprives you of meaningful options.
There is a separate version of free will that insists that agents are the ultimate cause of their actions, rather than mediated causes, which would not be consistent with determinism. But that is not the only definition of free will (and I don't think a very common one, except by incompatabilists).
A lot of this hinges on what people actually mean by the individual phrases.
If you sometimes engage in deliberation, and sometimes deliberation changes your mind, then even if that deliberation would have always inevitably come out the same way, you still know that in those cases deliberation affected your subsequent actions. Your deliberation (informed though it may be by external factors) is sufficient for most sensible versions of agency.
https://plato.stanford.edu/entries/compatibilism/
Classical free will, going back to Hobbes, is really just that sometimes we act unencumbered by external forces. Determinism posits that no one can act other than how one ultimately does.
Those could be compatible.
There is a difference between me deciding to stay in a room after careful deliberation, and me being chained to a wall in that room in spite of my protest.
Even if the future is fixed, there's still a difference between a person being forced to do something by an external actor and a person doing something they would ordinarily do.