In the months ahead of Halloween this year, we talked a bit about a project called Legizmo Kincaid by lunotech11 that could be used on jailbroken and non-jailbroken devices (the latter via TrollStore) to pair Apple Watches running newer versions of watchOS with older versions of iOS.
Legizmo Kincaid launches on Chariz, letting jailbreakers on iOS 15 pair unsupported Apple Watches