I'm very sorry to hear that. That's always the fear when a GI cancer patient has an obstruction. I know I was terrified when my husband had his SBO but it resolved on its own without surgery, which it would be very unlikely to do if it were due to tumors invisible to CT (he had CTs and conventional X-rays that didn't show any masses, but as we know sometimes peritoneal mets don't show up on CTs). Depending on the burden, a cytoreductive surgery may work, though with the progression in the other areas that may be more questionable.
PS You should look into clinical trials. I don't know what information is specifically available for Germany, but you can go to clinicaltrials.gov and select by country to see only trials that are or may be recruiting in Germany.
D/H Dx 10/2019 RC age 61
Clinical T4bN2M1a (common iliac and para-aortic lymph nodes)
MSS KRAS G12D
CRT 11/19-1/20 FOLFOX 3/20-7/20
Pelvic exenteration w/LAR 8/20
ypT4bN0Mx G3 0/14 nodes LVI not seen PNI-
CEA 10/19:20, 1/20-11/20:1.6, 4.3, 3.4, 2.7, 2/21:9.0 3/21:18,40 4/21:28,19, 5/21:13.3,8.6
PET 3/21 recurrence in distal nodes, L5 vertebra, pelvis