No wlan call on murena fairphone 4

Hi ladies and gentlemen,
I am owner of a new Fairphone 4, preinstalled with /e/OS, purchased from the /e/ shop.
I installed surfshark VPN from the /e/ appstore.
I am generally very pleased with the phone and the overall concept.
But I have one major issue: wlan call does not work (with or without VPN, and under all plausible VPN configurations, e.g. having the phone app bypass the VPN. I used the same provider / SIM card in my iPhone before and could use wlan call (even in flight mode and activated WLAN).
If I switch in flight mode and activate the WLAN (checking that it runs by using the browser) and try to make a call I get he error message: deactivate the flight mode or establish a wlan connection.
It is a klarmobil contract using the german D1 and D2 networks.
Some technical information:
After purchase I updated twice to /e/OS 0.23-20220413178020.
the preferred network type is set on NR/LTE/GSM/WCDMA (as preconfigured)

Can you help?
Best regards

Regain your privacy! Adopt /e/ the unGoogled mobile OS and online servicesphone

Hi Jo,

Someone has made a bug report for this.

Note the link within to further discussion on FP forum.

Hi Chris,
thank you very much! I attached my problem to the bug report, you mentioned. Seems to be the same Bug.
Best regards