Versions of Numbers object

Numbers has autosave. But you can manually save by going in the menu to File > Save or typing command-s.

That's the same as in most Mac apps.

To retrieve previous versions (in the case, for example, where you change your mind about a change, you usually can recover the previous version before the change by going in the menu to File > Revert to > Browse All Versions ... and going back in time.

SG

If you want to save as...

click in the file menu, then hold the option key.

when you do this, the menu item "File > Duplicate" will change to "File > Save As…"

Also, see this and similar articles ...

https://www.macworld.com/article/673187/how-to-save-as-on-mac.html

SG