This would certainly indicate an issue within the software and not the web server. You could reach out to the MediaWiki team and see what may be happening or review their requirements for updating.Well, I reverted back to a version of the MediaWiki that supports both PHP 7 and 8.
Using PHP 8 was leading to the 503 error. I switched to PHP 7 from the control panel and the update script run without an issue!
I'm not sure why the error is thrown, as the latest version of the MediaWiki supports PHP 8.1+ and has dropped support for older versions, but anyway for now I will keep the version that works.
The same thing happened to me once working with wordpress, thinking about what it could be is going crazy, you have to be practical and move on, if it works then leave it like that hahaha
This would certainly indicate an issue within the software and not the web server. You could reach out to the MediaWiki team and see what may be happening or review their requirements for updating.