WLAN probs with raspi4, buster, and mm2

[drebes]

Hi @all ,
I’m a bloody rookie, so pls excuse if my questions are quite a bit rookiesk ;-)
I installed a raspi4 with raspbian buster - wlan is working - router is pingable.
Configuring ssh - wlan and ssh is working.
Now I installed MM2 ( bash -c ‚$(curl -sL https://raw.githubusercontent.com/MichMich/MagicMirror/master/installers/raspberry.sh)
Hey - it started :-)
OK lets do a reboot to see if it starts automatically - fine - but no ssh connection possible.
MM2 shows only ‘loading’.
So I used ALT-F11 to reach the Desktop and started a cli.
ifconfig shows no IP-configuration.
ifdown --force wlan0 works
ifup wlan0 seems to work, but - ifconfig shows NO IP-config and network not connected :-(
So I tried to force an restart regulary.
I wrote a script to restart the interface every 5 minutes - but it fails. (for sure if even ifstart --force doesn’t work)
Now I’m somehow in a deadend.
I’ve got further idea how to get this damn wlan working :-(
Any idea?