Irregular plural keywords? How do they rank?

If a keyword is an irregular plural how does this affect ranking?

Example "shelf" 500k searches and a KGR of 18 but shelves also has 500k due to google seeing it as the same word BUT its KGR is 0.60 how does this affect my site ranking?

Does Google show different results for each word if so how do I know how many searches the plural keyword is getting? Also, will the plural keyword (Shelves) be competing with sites ranking for shelf?

(Fake keyword & Numbers are being used its just a made-up example)

Google knows the intent of search with missprelled words and thus search results are the same.

There’s no difference if it’s shelf or shelves.