It’s a little more complicated that this:
It is possible to program a beta range for turboprops. The SimWorks Kodiak and the Milviz PC-6 Porter are examples that implement this in a slightly different way - for both of them you can define a button on your throttle control to switch into beta mode, and then when you move your throttle it will go first into beta and then into reverse mode.
Had the engine of the Iris PC-21 been programmed as a turboprop, then it would have been technically possible to implement a beta range. However, the PC-21 also has this automatic torque compensation feature - on takeoff roll, the aircraft doesn’t pull to the left like a regular 1,600 hp aircraft would. To make this happen, the Iris developers chose to program the PC-21 engine as a jet engine, not a turboprop engine. And with a jet engine you can’t implement a beta range.