Unknown collation: 'utf8mb4_0900_ai_ci'

This error message indicates that a collation with the name 'utf8mb4_0900_ai_ci' is not recognized or supported by the database or application you are using.

Collation is a set of rules that determine how data is sorted and compared in a database. 'utf8mb4_0900_ai_ci' is a collation introduced in MySQL 8.0.4, which supports the full Unicode character set and implements the "accent-insensitive" and "case-insensitive" comparison rules.

To fix this error, you may need to upgrade your database or application to a version that supports the 'utf8mb4_0900_ai_ci' collation, or change the collation of the affected database or table to a supported one. You can check the list of available collations by running the 'SHOW COLLATION' command in MySQL.