It's common for SEO plugins to offer the option to noindex pages.

Catch this and do not submit newly published noindex pages to IndexNow.

• Yoast SEO
• AIOSEO
• Rank Math IndexNow included in free plugin, recommendation not to install covers this.
• Any others I should be aware of....

Both Yoast and AIOSEO use the legacy meta boxes, may need to modify how these are checked.