I have just one comment to add about your database default collation. Looking at your error message "...(utf8mb3_unicode_ci,IMPLICIT)...", Your database is set use utf8mb3_unicode_ci by default, which is the collation that will be used when creating something new (database, table, column) without specifying the collation.
I don't think the conversion tool can change that. But you have to change it to utf8mb4_general_ci to avoid futur troubles. You can use phpMyAdmin or directly change the value for "collation_server" in your MySQL configuration file.