I have not read this discussion in detail but just to address the screenshot in first post and Braden reply: we actually have two different boot error messages. One says "Details have been logged to the Flarum log file" while the other says "Details have been logged to the system PHP log file" (source).
When the second message is seen, nothing is logged in Flarum log file because it means the error prevented Flarum from ever reaching the code that opens the log file. Usually it's related to PHP version or extensions, PHP warnings or deprecations, or file permissions.
