You will need an authentication method list for enable. If you are using local database, it would look like this:
SSH@ICX(config)#aaa authentication enable default local
If you are coming from 8.x releases, there are a lot of changes in authentication with 9.x. The 9.0 release notes will list new, modified and deprecated commands. The respective guides would then have the details on said new commands.
Ben Beck, RCNA, RCNI, Principal Technical Support Engineer support.ruckuswireless.com/contact-us
Is there a way to just have an enable password? The documentation says this (emphasis added),
If enable authentication is configured on the device, when a user attempts to gain Super User access to the Privileged EXEC and global configuration levels of the CLI, by default the device prompts for a username and password. You can configure the device to prompt only for a password. The device uses the username entered at login, if one is available. If no username was entered at login, the device prompts for both username and password.
I do have username at login, as you can see from the output I shared, but it still asks for a username.