@lduboeuf Yes, I checked them. They should be web.vodafone.de and they are.
For reinstalling UT I got back to Android and installed UT from there. While on Android the mobile data worked just by activating it.
Is there anything else to be checked?

After reinstalling UT the problem persists. Shall I submit a bug?

On the weekend I updated to OTA8 and the problem is as before. Does anyone has any good ideas?

@Vlad-Nirky
Sorry for the late reply. I tried to follow the steps of post #2 but I couldn't complete them:

stop network-manager

sudo systemctl stop network-manager
Failed to stop network-manager.service: Unit network-manager.service not loaded.

/etc/init/ofono.override

sudo /etc/init/ofono.override
sudo: /etc/init/ofono.override: command not found

@lduboeuf Thanks. Any other ideas?

@kugiigi I'm sorry for providing the wrong answer yesterday. It's the same like in your picture: Activating cellular data brings the dots in the Wifi icon.
@lduboeuf Never used that too and output of

systemctl --user status batterysaver.service

is

Unit batterysaver.service could not be found.

@kugiigi I'm not sure if I understand your question correctly. When mobile data doesn't work, the only effect is that the button for mobile data moves to green. Beyond that I cannot see anything happen.

On my Fairphone 4 with Ubuntu Touch 20.04 OTA-7 and a german amiva (Vodafone) SIM mobile data doesn't work.
It's a used phone and I think I tested the mobile data with Android.
At one time with this Ubuntu installation mobile data worked. But after a power cycle mobile data is gone again.
I tried another SIM card from congstar (Telekom) and mobile data doesn't work either.
Both SIM cards work on other phones with Android.
Airplane mode on and off, Data roaming on and off doesn't have any effect.

I tried serveral ofono commandos and I think here is the problem:

activate-context

gives this Error message:

Error activating /ril_0/context1: org.ofono.Error.NotAttached: GPRS is not attached

I attached the output of

list_modems

Could anyone help?
list_modems.txt