I see that you have a standard router version, which has required Band support for o2 Germany. So unless you are out of coverage for all 2G/3G/4G bands - which is very unlikely - it should find and connect to o2.
Having said that, and knowing that you have already spent substantial amount of time, i still must ask some basic questions:
- the SIM card that you use in RUT950, does it connect to o2 and establish Data Connection if inserted into a smartphone, in the same location?
- do you have both LTE antennas connected? (sounds obvious, i know)
- which firmware versions have you tried exactly?
Here is what i suggest as a followup:
- flash newest firmware available at https://wiki.teltonika.lt/view/RUT9xx_Firmware. Unless you already got it;
- make a Scan for Mobile Operators (as per your attachment) and hit Auto Select
- afterwards under System -> Administration -> Troubleshoot download a Troubleshooting file (full package). Do not paste it here in public chat;
- after all that you could make a factory RESET (if haven't done that before) and check results;
Without further investigation it is not possible to know what is amiss with your device, so ping me via PM, attach the downloaded Troubleshooting file, and we can take it from there.
Shall be awaiting for your reply,