ssh-keygen has supported the -Z flag since 1.237 of ssh-keygen.c. However, and man page has never been updated to include the specifics of the operation of this flag. Please update the man page for ssh-keygen to include the specifics for the "-Z" option, which allows you to specify the encryption cipher for a private key. Based on the code, this option only applies if you are using the new private key format, either currently used if you specify the -o flag when creating/updating a key, or specify ED25519 for the key type.
Created attachment 3458 [details] Document ssh-keygen -Z and provide better error on incorrect arg.
Created attachment 3459 [details] Document ssh-keygen -Z and provide better error on incorrect arg. fix a couple of "z" that should have been "Z"
The patch has been applied and will be in the 8.5 release. Thanks for the report.
closing resolved bugs as of 8.6p1 release