Thanks for reviewing my schematics.

I have now reworked a few things.
1. I supply the VDDIO_18 pin with 1.2V (using the chips power supply)
2. Checked if the crystal oscillator is still working with 1.2V and it is.
3. 0.8V supply is generated from the 1.2V. So, if the power supply is switched of, the VDDIO supply is also off.

I think from the electronic point of view, I'm probably using the chip well within its specs.

But I still don't get any response from the ASIC.

I'm open for every other clue