WordPress error after installing plugin “Internal Server Error” [closed]

Could you please try to deactivate all other plugins, revert to a default theme like TwentySeventeeen and test once more? If this resolves the error, it should be a conflict with some theme and/or plugin(s). Simply activate them back one-by-one checking each time the installation process until you get the error again.

Also, check that you are running the last version of WordPress.