MySQL 8.0

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CREATE TABLE data (
  id INT AUTO_INCREMENT PRIMARY KEY,
  genres VARCHAR(255)
);

INSERT INTO data (genres) VALUES
('Classics, Fiction, Historical Fiction, School, Literature, Young Adult, Historical'),
('Fantasy, Fiction, Young Adult, Magic, Childrens, Middle Grade, Classics'),
('Classics, Fiction, Romance, Historical Fiction, Literature, Historical, Audiobook'),
('Classics, Nonfiction, History, Biography, Memoir, Historical, Holocaust'),
('Classics, Fiction, Dystopia, Fantasy, Politics, School, Literature');

WITH cte AS (
  SELECT id, REPLACE(genres, ', ', ',') AS genres
  FROM data
)
UPDATE data JOIN cte USING (id)
SET data.genres = CONCAT_WS(',',
    IF(FIND_IN_SET('Classics', cte.genres), 'Classics', NULL),
    IF(FIND_IN_SET('Fiction', cte.genres), 'Fiction', NULL),
    IF(FIND_IN_SET('Literature', cte.genres), 'Literature', NULL),
    IF(FIND_IN_SET('Young Adult', cte.genres), 'Young Adult', NULL),
    IF(FIND_IN_SET('Fantasy', cte.genres), 'Fantasy', NULL));
      
SELECT * FROM data;

Records: 5  Duplicates: 0  Warnings: 0

Rows matched: 5  Changed: 5  Warnings: 0

id	genres
1	Classics,Fiction,Literature,Young Adult
2	Classics,Fiction,Young Adult,Fantasy
3	Classics,Fiction,Literature
4	Classics
5	Classics,Fiction,Literature,Fantasy