Tbh I dont think that this is actually incompatible with determinism, since the mechanism by which the future is predetermined doesnt necessarily have to be that all causes only have one possible effect associated with them. I mostly suspect the universe is deterministic because I suspect (though this is only a suspicion that I cannot prove) that the universe has block time and therefore that, even if random events with no clear "this must lead to that" chain exist, the future is predetermined merely by "already" existing along some time axis. Sort of like how if you had a character in a flipbook roll a die, and nothing earlier in the flipbook forces the die to have to land on one particular number to keep the plot self-consistent, the outcome of the die will still always be the same, because the pages where its result is shown already have been drawn.