Is there a simple way to remove all the category info / text from top of page?

Product Support
2

Shouldn’t be displayed if you add the following to the common CSS of a theme component:

ol.category-breadcrumb {
    display: none;
}
#navigation-bar {
    display: none;
}

I created a simple little TC for you that you could install locally to do it for you:

discourse-hide-nav.zip (1016 Bytes)

Go to your Discourse admin panel > Customize > Themes > Components > Install > From your device
Choose discourse-hide-nav.zip then click Install
In the Hide Nav TC editor click ‘Add all themes’ then click the green check circle

edit: Steven’s reply below is preferable imo