Am I missing something? 

I can't seem to get a Database Filter Block, to work on a database with no categories. 

I can drag it out on to the page, but it won't show up.

JM

 

Should work. I use that: https://www.typografie.info/3/Schriften/fonts.html/

And technically, categories can’t be turned off. If they are off, it means internally there is one, which, when opened, behaves just like if there were others. 

Normally, for the filter block to appear, there are two conditions: You actually have fields which were set to be filters. You are on a listing(!) page. No other page is supported, including the front page.