there is any way to use swift for the dsp part of an auv3?

No. You shouldn't call any objective-c in the dsp code either. Your dsp code shouldn't allocate any memory. Neither Swift or Obj-C can guarantee that memory is not allocated when a method is called.

For what it’s worth, I have done it - my real DSP code is in Rust, but to shorten development time when tweaking an algorithm, and the performance was fine. BUT, I was emulating what I do to make Rust callable by an audio unit - that is, everything is raw pointers and primitives, and there’s no allocations because the DSP contains no code that could possibly allocate. So it’s basically writing C in Swift. You can do it, but you can’t use any of the things that make Swift pleasant to use.