If you don't want to buy one, you can rent a Mac in the cloud only when you need it (unrelated to Xcode Cloud) for 0.10€ per hour at Scaleway
[0] On the Scaleway checkout for the Mac Mini M1, at the bottom: "As required by Apple License, you must keep this Instance for at least 24 hours. You will be able to delete it only after 24 hours.".