1. Make sure your data is backed up if you want to keep any data
2. Make a Windows 8.1 installer drive and run it
3. Install Windows 8.1 on top of the current OS (or partition if you are looking to dual boot)
4. Windows update should look for a compatible driver automatically for UHD Graphics 605
5. If not, go to ****** and search "UHD Graphics 605 drivers Windows 8.1"
6. Download the driver from the official Intel page (I know it doesn't say Windows 8.1 but technically, it should be backward-compatible) and install
The worst case is it won't work efficiently where you might run into glitches --> repeat steps 1 and 2 but make a Windows 10 installer drive to reinstall Windows 10.
Side note: Windows 10 is much more energy-efficient tho and built-in software are better managed and nicer interface, why do you despise it for?
