Fresh Install Theme and Plugin Update Issue

Hi,

New user with a fresh install.

When I try to install new themes/plugins from the admin panel they appear to start the process but fail; a red "box" appears briefly at the top right and disappears before I can read it.

Is there an error log somewhere?

Thanks,

Brad

Ok, I was activating a new theme uploaded through the manual installer and got the following error and seem to have lost the whole admin panel.

https://ibb.co/Jnxqf1Y