ALTER USER 'doadmin' IDENTIFIED WITH mysql_native_password BY 'secret_password';
Change ’secret_password‘ to the password given to you by DigitalOcean.
The reason behind this is that SequelPro and other MySQL Clients only work with the old (5.X) way of MySQL authentication vs. the new (8.X) caching_sha2_password. It has nothing to do with the MySQL version itself as Sequel Pro seems to work just as well with version 8.X. You can find more information in the MySQL documentation.