Your new MacBook Air should be running macOS Sequoia v15.3 (or updated to it), and Pages v14.3.
Your Apple Mail options for attachments from Pages are:
With this current version of Pages, if you want your saved Pages document to be automatically attached to a new Apple Mail compose window, you select File menu > Share… > Send a Copy and choose Mail from that menu.
If you want your Pages document to be converted to another document format and automatically attached to an Apple Mail compose window, then you use File menu > Export To > ____ and then select Send a Copy and Mail.
Drag and drop the saved Pages document onto an Apple Mail compose window, or use the previously mentioned Export To option and select the Save… button to produce that export format document on your filesystem. Then you drag and drop that document onto the Mail compose window.