Try drivers from this list: Downloads for Intel® HD Graphics 520
Otherwise go to pcsupport.lenovo.com/de/de/products/laptops-and-netbooks/thinkpad-yoga-series-laptops/thinkpad-yoga-260/downloads
Try their video drivers.
Check if BIOS is up-to-date.
Did you install the "Adaptive Brightness Registry Patch" from Lenovo?
I tried all you sent with no success.
I am having the same issue with the Intel HD Graphics 520 driver on my Yoga 710. I have also noticed that the color temperature randomly alternates between cool, blue tones and warm, orange tones despite disabling both night light and dynamic brightness control.