Hello,
is there a possibility in openWRT to display the LAN structure in a topology map?
So that you can see the history of all devices in the LAN?
Like e.g. with unifi devices or AVM Fritzbox?
Thanks 
There is no such feature in OpenWrt. FWIW, the Unifi map is not perfect (and until recently, it was often broken).
This type of feature would require the existence of a standard (and open) reporting protocol of what is connected to each port of device, and then there would need to be a way of displaying that information in a GUI -- these are both not trivial. Unifi works best if you have a full Unifi stack because UI has implemented both a protocol and a GUI for this -- but these are not open and not compatible with other brands.
I have not tried it, but it is possible DAWN has something of this nature (I honestly don't know if it does or not).
Alternatively, although it won't really be a topology map in any way, you could just look at the arp tables to know what is connected.
No DAWN doesn't do that. It has a summary of which clients are connected to which AP across the network, but not how the AP link back to each other.