The new iOS 15 and iPadOS 15 lets you create a shareable link in the FaceTime app that allows you to chat with anyone, even Android users
According to Popular Science it's as easy as this:
Open the built-in FaceTime app, tap Create Link at the top of the screen, and you’re basically done. You can stick with “FaceTime Link” or go into Add Name to give it a unique name like “very cool party.”