Migrate database from one server to another without downtime
In general I don't think it's possible to move a database without any downtime with MySQL standard tools.

However you can try to use mysqldump and mysqlbinlog to minimize "data loss": see section "Example: mysqldump + mysqlbinlog for Backup and Restore" in https://dev.mysql.com/doc/refman/8.0/en/mysqlbinlog-backup.html