Didn’t know if I could submit an issue for this on GH, so I figured I’d post here.
Consul gossip encrypt key (consul keygen) creates a 32-byte key, which was upgraded from a 16-byte key in 1.6.0 (shows up in Improvements in 1.6.0 changelog).
The learn platform states that it is a 16-byte key, which conflicts with the Consul documentation