Install Plugins - install.php - "Uh oh"
When running install plugins the page returns "Uh oh".
Firebug shows - 500 error on ajax.php POST - "action:installDataTypes"

I had this issue when I edited the regional names file (NamesRegional.class.php) restoring a previous version resolved this issue. I wanted more names in the file.
Installing on MacOS High Sierra with PHP 7.4.5 and Apache 2.4.43 getting this Uh-oh too.
I was getting this on Windows 2016 with PHP 5.4 and IIS 10.
For me, it was working for Data Types, but failing on Export Types. This ended up being addressed by removing the Excel plugin directory from \plugins\exportTypes. I don't need Excel, so I have just left this removed and carried out without it.
Worked around to install by:
- Change file permissions to rw for all (temporarily).
- Replace all occurrence of get_magic something function to false in all files (this function is deprecated and should return false anyway).
- Restored file permissions.