Earlier for SSH and WinRm deployments, in Select Nodes step user can choose to deploy specific hosts and choose from a list of hosts added previously in Infrastructure Definition.
Now you can specify hosts which are not present in Infrastructure Definition. Doc reference is here
User can also choose hosts which are not defined in Infrastructure Definition for SSH deployments on Start New Deployment screen with the option to target specific hosts enabled.
Doc reference is here
This is behind a feature flag: