Hi Audioniek,
thank you for your great support. First of all, for the DVB-T(2) issue: On my tuner it says DNOQ44QCH106A, so it seems DVB-T2 ready. This is confirmed by the original Octagon software, which indeed does tune in to channels in the new DVB-T2 standard. Unfortunately, this works with neither HDMU, Audioniek nor Bpanther's Neutrino images, which all return "no channels found" on the DVB-T2 frequencies. In the end, all these images seem to rely on the same driver from the Duckbox project (stored in the cdx2820.ko kernel module), so I guess this driver is the issue. Even though the source code (e.g. "cdx2820.c") refers explicitly to DVB-T2, the corresponding implementation seems buggy or is not active. The driver posted above by pop1234 seems to be different from the Duckbox project, and it is not obvious to me how to migrate it to sources relying on Duckbox.
Please correct me if I'm wrong.
Now for the DVB-S(2) issue: Thank you, Audioniek, for your extensive tests. I really don't understand what is going on. I can tune in to vertically polarized Astra 1E channels (e.g. KiKa HD) with the original Octagon, the latest HDMU from 2017 and Bpanther's image from 2020. It does not work with your precompiled atevio7500 Enigma 2 image and compiling it manually did not solve the issue either. I will try whether I can overwrite the avl2108.ko module from your builds with versions from other images.
Edit: Just to make sure it did not get lost in the noise: