composer data not shown on page

We are trying to build pages with composer forms in order to quickly setup project data. In a recent post of another student I learned that all components need to be installed properly in order to make composer pages work.

When I try to map a composer control block to the page area – area names are matching – I get a white dialog box with no choice of blocks. When I click «add» this error shows:

Exception Occurred: /home/httpd/vhosts/sys.null.net/bbx.031/concrete/src/Page/Page.php:2823 Call to a member function getPageTypeComposerFormLayoutSetControlID() on null (0)

We are working with DaveDew’s Atomik Clone on 9.3.9. Everything else works just fine. Looking in composer of the page I see all desired fields, but they don’t show on the page itself. On the pagelist though I see the entries.

Is that the problem?

I don’t understand the difference between default Atomik installation, where everything works and an Atomik Clone installation. I thought it is the same.