You may come across a similar error like below when importing a database dump.
Unknown collation: 'utf8mb4_0900_ai_ci'
The problem originates from the MySQL or MariaDB version difference between the source server and where the dump is being restored.
Apply the following command to replace the character set in the dump file before importing it.
sed -e 's/utf8mb4_0900_ai_ci/utf8mb4_unicode_ci/g' -i myfilename.sql