Today we figured out that the Raspberry by can work on a Dual band modem (2.4-5). However Band steering needs to be turned of completely. This feature in your modem pushes all traffic to the least congested band > 5Ghz. The Raspberry doesn’t support that.
We are in a corporate network here and cannot change these settings.
We will try to use a Dual-band usb stick.
To be continued.