I’m running the first beta of iOS 14.
Hopefully the picture shows.
I think the back to is only supported on phones which have tap to wake. When your phone is locked and the screen is off tap on the screen once. If it wakes up the screen then your device support tap to wake. If it supports that I think it should support the double/triple tap feature on the back of the phone. I headed this mentioned in one of the beta reviews I watched last week but I cannot remember the full details off hand. I am fairly certain that tap to wake means there is support for the double/triple tap.