I posted some more info about ONNXmutable in the announcement thread.
Tl;dr is that ONNXmutable pretty much only uses the protos from ONNX.jl, so aside from some annoying warnings from the deprecated DataFlow package ONNXmutable is fully functional (barring stated limitations and yet undisovered bugs ofc) and a model which can’t be loaded in ONNX.jl might very well load with ONNXmutable.