Separate windows in Numbers

Note that a new document opens in a new tab only if you have told your Mac to do that in System Settings. You can tell your Mac to open in a separate document if you want.

"Prefer tabs" can be useful when running apps In Full Screen but usually I don't want that behavior. Hence my setting above. That saves having to drag a tab into its own window out each time

If you're not yet on Ventura then you will find a similar control in the old System Preferences.

SG

when you open a new file it normally opens as a new tab in the main Numbers window, you can drag a tab out and it will open in a new window proper, which I think is your ask.

Jason

File/Open

or

Click on the other file in Finder to open it

You can have multiple documents open at the same time, just not multiple views of any single document.