Yes I tried to do a Group FaceTime call with family yesterday (roughly 10-15 devices). I’m on iOS 13.7 and I noticed that I couldn’t add devices with iOS 14.2 or later to the group, they were grayed out even though their FaceTime settings were setup properly. I could FaceTime them only with another iOS 14 device. In the end I switched to a zoom meeting, it was so much easier to get everyone on board plus they could use their laptops, chromebooks or whatever device they want. I can see why zoom is so much more popular