Your App Store page has a field nobody can see

• Apple gives every app a hidden Keywords field: up to 100 characters. Users never see it, but App Store search uses it.
• Don't repeat words that are already in your app name, subtitle or category.
• Separate keywords with commas and no spaces. Spaces inside a phrase are fine.
• Skip plurals of words you already have, and filler like "app" or "the".

Source: Apple: App Store search (developer.apple.com/app-store/search) and App Store Connect help (keywords up to 100 bytes)