This is the fundamental strong point of blocsapp (and bootstrap/responsive sites) - being able to adapt to form factors according to the device width.
There are little icons in blocsapp where you can switch between desktop, tablet and mobile views. Similarly, you can select an element and in the attributes panel you’ll see those same icons and you can turn the visibility of that element on and off for a specific form factor.
Designers just don’t design one site and it fits all form factors. A mobile site will often have different content to a desktop site (usually a reduced content on a mobile site, or diferrent visuals/presentation).
For the navigation, create one bloc that is visible in desktop and tablet only and another bloc that is visible in mobile only.
This technique is not blocsapp-specific.
We can all say that about any software that we are familiar with versus software we aren’t very familiar with.
For the navigation issue, the blocsapp navigation panels do the heavy lifting for you. Blocsapp is built on bootstrap, so if you stray off the supplied path then a little more work is required. It’s the same for all software, and life in general.