I’d like to recommend vvvv. It’s a node-based version of C# that is always runtime. The edit-compile-run loop is eliminated so you can tweak both constants and behaviour instantly. For a processing-like drawing interface I’d recommend the built-in Skia library which I think processing is modelled after. VVVV overall is definitely a steeper learning curve, but it’s very powerful as you can use any .net libraries, 3D graphics, shaders and much more. Shaders in particular is a great tool that lends itself to a dataflow representation.

Touchdesigner is more popular and I suppose declarative, but vvvv is more general purpose and similar to the processing workflow. It’s a very weird tool I’ve used for everything between MIDI instruments, live installations, escape rooms, VJ rigs and, well, proc art.