Two years later it's still not compatible... it's a bit of a disappointment
That device was discontinued by Apple a year ago. According to https://support.sonos.com/s/article/3222 Sonos have no intention of ever supporting it.
They don’t list the latest generations of iPad Pro in the article, which implies that those are supported.
Already have an account? Login
Enter your username or e-mail address. We'll send you an e-mail with instructions to reset your password.
Sorry, we're still checking this file's contents to make sure it's safe to download. Please try again in a few minutes.
Sorry, our virus scanner detected that this file isn't safe to download.