As mentioned here, luci-proto-qmi is missing the option ‘pdptype’ in the GUI. Without it, it isn’t possible to configure the IP standard the WWAN-card has to use.
The error itself is also present in the /etc/config/network file, because as soon as you add the option to the QMI interface manually, the WWAN connection doesn’t work anymore. Right now, only IPv4 is possible.
A patch for the first problem is already available upstream, but I’m not sure, if it’s the final solution or if there are some missing bits left.
Referenced commit leads to the forked repository. Fortunately, this guy submitted his changes to the upstream repository, and indeed it is included in OpenWrt.
That’s great, thanks for the fast response! When or how will this be included into wherever it needs to be included so that it comes to my Turris Router?