Steps to reproduce the issue

Came across this while testing the privacy consent plugin. The easiest way is to $query->dump() the query in https://github.com/joomla/joomla-cms/blob/3.9-dev/plugins/system/privacyconsent/privacyconsent.php#L513

Expected result

SELECT `r`.`id`,`r`.`user_id`,`u`.`email`
FROM `cxicl_privacy_consents` AS `r`
LEFT JOIN `cxicl_users` AS `u` ON u.id = r.user_id
WHERE `remind` = 0 AND DATE_ADD('2018-09-08 14:36:27', INTERVAL -323 DAY) > `created`

So the date in DATE_ADD quoted.

Actual result

SELECT `r`.`id`,`r`.`user_id`,`u`.`email`
FROM `cxicl_privacy_consents` AS `r`
LEFT JOIN `cxicl_users` AS `u` ON u.id = r.user_id
WHERE `remind` = 0 AND DATE_ADD(2018-09-08 14:36:27, INTERVAL -323 DAY) > `created`

Date in DATE_ADD is not quoted.

Additional comments

Looks like this issue is caused by this PR #21844, that removed the quotes around the date in the string returned.

//cc @alikon