Sounds like you’re doing the right things to get more information. You’re probably just encountering a situation where the standard mechanisms for reporting issues are not being used well enough to collect anything helpful.
Are you sure you edited the appropriate config.ini (i.e. local/config/vufind/config.ini, rather than config/vufind/config.ini)? That might explain why manually entering the SQL failed.
However, I’m not sure why “skip credentials” would give you an error message. That’s supposed to generate all the SQL commands without connecting to the database so that you can copy and paste them. It does make use of the database connection object in order to do escaping properly… so one possible explanation might be that you’re missing the Mysqli extension to PHP, and that is the cause of all the exceptions. If that’s the case, we should probably make the code smarter so that it can offer a more targeted explanation of the issue.
If that still doesn’t sort things out, the next step is to put some debug output into the catch block of module/VuFind/src/VuFind/Controller/InstallController.php’s fixdatabaseAction() method.
Let me know if you need more help, or if you come up with any enhancements to save others from falling victim to this same problem.