We’re already past those days where non-destructive photo-editing is exclusive to Adobe Photoshop. Paint Shop Pro probably has it. But, certainly Photoflow, Affinity Photo, Krita does. And non-destructive editing always applies changes. No need to flatten to see changes.
Non-destructive editing is not exclusive to having adjustment layers. You can have adjustment mask ala smart filters in Photoshop, or adjustment mask in the form of Affinity Photo or Krita. There’s file layers, transform masks, and clone layers. All of those are essentially things that are non-destructive. Also, non-destructive layer effects counts too.