Occ db:convert-type fails to convert

nextcloud 30
nginx
previously working install that got buggered up during the upgrade from 30.0.5. finally almost working and decided for perverse reasons to switch to mysql.

An unhandled exception has been thrown:
Doctrine\DBAL\Exception: Failed to connect to the database: An exception occurred in the driver: SQLSTATE[HY000] [2002] No such file or directory in /usr/local/www/nextcloud/lib/private/DB/Connection.php:233
Stack trace:
#0 /usr/local/www/nextcloud/3rdparty/doctrine/dbal/src/Connection.php(458): OC\DB\Connection->connect()

the database is there and accessible

nextcloud@localhost [(none)]> use nextcloud;
Database changed
nextcloud@localhost [nextcloud]> show tables;
+-----------------------------+
| Tables_in_nextcloud         |
+-----------------------------+
| oc_accounts                 |
| oc_accounts_data            |
| oc_activity                 |
| oc_activity_mq              |
| oc_addressbookchanges       |
| oc_addressbooks             |
| oc_appconfig                |
| oc_appconfig_ex             |
| oc_authorized_groups        |
| oc_authtoken                |
| oc_bruteforce_attempts      |
| oc_calendar_invitations     |

Hi @paulbeard, unfortunately a lot of information to help you is missing as you ignored the required support template. Please edit into your post and add as many information as possible. This will give us the technical info and logs needed to help you!