The plural of quiz is quizzes.
1. A short and informal test or exam. 2. A game or competition in which one's knowledge of a subject is tested.
The plural of quiz is quizzes.
Sometimes English words add an extra consonant when forming their plurals. In this case, the word adds an extra -z to the stem of the word to form its plural.
Unfortunately there are no strict rules about this in the English language and so a lot of plurals simply have to be memorized.
Singular Example: Did you study for the mathematics quiz this afternoon?
Plural Example: Despite our poor general knowledge, we often go to pub quizzes on Wednesday evenings just for fun.
Pub quizzes in the UK have been a popular pastime dating as far back as 1961.
Sources:
https://dictionary.cambridge.org/dictionary/english/quiz
https://boakandbailey.com/2020/04/when-did-pub-quizzes-become-a-thing/