Facetime no longer working between 13.4 and iOS 9 devices

Facetime no longer working between 13.4 and iOS 9 devices

Due to Corona distancing and quarantine my 89 year old mother is using an old iPhone 4S for facetime with the whole family worldwide. It all worked great until I upgraded my iPhone XS to iOS 13.4 yesterday. All family members with 13.4 are no longer able to connect to iOS 9.

Facetime tries to connect but without success.

Really good timing Apple. head shaking.