Less and fewer
Fewer means “not as many.” We use fewer with countable nouns like cookies.
Less means “not as much.” We use less with uncountable nouns like milk.
https://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-26434.php
https://www.myenglishpages.com/site_php_files/grammar-exercise-fewer-less.php
https://www.gingersoftware.com/content/grammar-rules/adjectives/fewer-vs-less/
https://www.englishgrammar.org/less-and-fewer/