When you run an update, either from j3 to j4 or within the J4 series, there are several steps (very simplified)

1. upload and extract files
2. check for and execute any sql updates in com_admin\sql
3. log the sql run in the joomla_update log
4. check for and remove any files in com_admin\script.php
5. Report Successfully Updated

But this is not true
if a single sql command fails at step 2 nothing is logged and we jump directly to step 5
This is obviously not correct and very misleading

If the error occurs during an update from 3 to 4 then the only way to recover is to resort to a backup because althugh you have the success message you have both j3 and j4 files because step 4 was skipped

PS Only successful queries are logged in the joomla_update file