As long as you still have the Routines tab available in the SmartThings Classic app, you can create new Routines. 
Some users have found that if they delete all Routines, then the tab disappears and there’s no way to get it back (unless you reach out to SmartThings support and request they add it back).
Similarly, SmartThings has started prompting some users with a banner in the Classic app that runs a transition/migration to equivalent ‘new’ app features. Among these migrations is a conversion from Routines to Scenes. It’s a one-way migration and Routine functionality gets removed as part of the migration.