With MySQL 8 (e.g. 8.0.19), looks like MySQL57Dialect is selected instead of MySQL8Dialect. Wrote a test that was examining the connection metadata:
... INFO ... HHH000400: Using dialect: org.hibernate.dialect.MySQL57Dialect
...
... INFO ... Database server : MySQL 8.0.19
... INFO ... Database driver : MySQL Connector/J mysql-connector-java-8.0.19 (Revision: a0ca826f5cdf51a98356fdfb1bf251eb042f80bf)