Nextcloud looks pretty confident that their db:convert tool will convert your database:
https://docs.nextcloud.com/server/18/admin_manual/configuration_database/db_conversion.htmlMy assumption is that the username and password should be the values used when you created the new database.
If you're using a non-standard version of mysql, you may need to customize the value of "--port", customize the settings for the mysql service, or both (The
mysql5.7 contrib needs some re-configuration after installation before it will respond on a TCP port)
If you installed Nextcloud using the SME
Nextcloud contrib, make sure the username and password for your database match the values in the configuration db (since those values will overwrite the values in the config file whenever you run
signal-event nextcloud-update).
On a VM, I'd make a backup before starting... On a physical server, I would locate the sqlite database and make sure I have a backup of the nextcloud application, configuration, data, and the sqlite database (just in case...). I used to move the actual content to a new/safe location, then copy it back to the original location before running updates on systems that made me nervous.