Yes, I did
pi@raspberrypi:~ $ sudo udhcpc -q -f -i wwan0
udhcpc: started, v1.30.1
No resolv.conf for interface wwan0.udhcpc
udhcpc: sending discover
udhcpc: sending discover
udhcpc: sending discover
udhcpc: sending discover
udhcpc: sending discover
udhcpc: sending discover
…
It just keeps sending discover messages without ever getting an answer until manually killed. The configuration with ifconfig wwan0 remains unchanged. I didn’t mention this command since I considered this not as the root of the problem but as a mere symptom. Of course, I might be wrong…
Meanwhile, I also tried this solution. Unfortunately, this stopped the wwan0 interface from obtaining an IP altogether. Seemingly, the default Raspberry Pi OS comes with only udhcpc as DHCP client, and disabling it disables DHCP entirely.