Bastiaan I have 7.1.1 so maybe that's why?
I would think an app is still able to tell Files which kind of files it would want to see. I mean it's a bit strange if Google would have only made a Files app which can only show images, right?
For example when I use the K9 Mail on my phone it uses the Files app too and it shows all kind of files and not only the image files. So there must be something that bunq does differently to tell Files to only show images when in the bunq app.