There is a new update that fixes this issue. As the game continues to improve, with the world becoming larger and more users continuing to ride, I do highly recommend upgrading.
We don’t have a boxed version (like old software you’d use to buy at Electronics Boutique or Babbage’s) where we can print minimum requirements on but they are available on our website. We can’t force you to read them and a giant pop-up that says “Hey! Make sure your computer meets these requirements!” every time Zwift starts seems like a less-than-ideal experience.
That being said, we make a best effort to help users with these machines run Zwift but progress marches ever onward. Our minimum requirement for MacOS has changed several times since older OS versions often stop supporting the updates we add as well.