Unfortunately the specs you detail are in no way compatible with a price below 900 euros, especially the 500+ GB SSD hard disk space.
The price for a 2in1 device with your minimum specs would be in the range of 1200-1600 euros with higher specs e.g. 1TB SSD or 16GB RAM going easily in the 2000+ range.
The best/newest in the market devices I would recommend would be:
1. Galaxy Book2 Pro: https://www.amazon.de/-/en/Sam…ows-raphite/dp/B09TWRJHXK
2. Microsoft Surface Pro 9: https://www.amazon.de/-/en/dp/B0BC9GCQNT/
For reference even the extremely old Microsoft Surface Pro 6 is above 1000 euros with such specs: https://www.amazon.de/dp/B08BZN77HR/