Keyword not set as well as some pages lack rich snipped

Hello,

Thank you for contacting Rank Math and sorry for any inconvenience that might have been caused due to that.
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​1. First of all, I am assuming that you have already changed the SEO Meta Title and Meta Description with the help of Rank Math:
Add a Meta Description in Classic Editor:

Add title and description in Gutenberg:

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​2. Then, ensure that this is the setting in the Schema tab if Rich Snippets are enabled on your website:
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​To reiterate, the Schema title must show %seo_title% and the description should show %seo_description% – this will ensure your SEO title and SEO Description that you set up via Rank Math can also be used for your schema details:
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​3. The next step is to check if your title/description is properly set up in the page source:
https://i.rankmath.com/HwXR1o

You can use this tool for the same as well: https://www.heymeta.com/

4. If it matches your settings, then you must check if Google has seen the changes already or not.
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For that, please check when the Google cache was updated for that page:
a.

b.

If the cache date is from before adding the new meta description, then you just have to wait for Google to re-crawl and re-index the page with the new info. If the date is after you made the changes,
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​Do note that if everything’s fine and Google still decides to show a different meta title/description for your search keyword, there is nothing you can do as Google sometimes ignores the custom meta info altogether and show something from the page’s content that matches the search intent better.

The best you can do is optimize your meta tags to try and match the intent of the search/keyword.

You can read more about it here

https://support.google.com/webmasters/answer/35624?hl=en

This section sheds light on that:

Why the search result title might differ from the page's <title> tag

Hope that helps. If you have any further question(s), please let us know. Thank you.