Pages v13.1 on Ventura 13.5 does not make any attempt to flag or correct extra spaces between words with any feature under Spelling and Grammar. Even Grammarly for Mac fails to catch every instance of extra spacing, skipping over two spaces and flagging the next occurrence further in the sentence.
The free WordService solution in the Mac App Store installs several Services during its installation — among them is Remove Multiple Spaces. Most of these services are not enabled and must be done by the user before they are active. I went to System [Preferences|Settings] : Keyboard : Keyboard Shortcuts… : Services : Text and selected the preceding Service name to enable it. Then it was available in the Pages Service menu for selected text.
I just selected the guilty text in my Pages document, went to Pages menu : Services : WordService: Remove Multiple Spaces and my selected text was immediately fixed.
I agree that Pages should catch extra spaces but since it does not, the preceding WordService solution will get the job done for any preselected text.