I am also curious what is this mystery update about?

Apart from an unanswered thread on Intel Community, Currently Google can not find any info about this...

Even the driver version does not match up with any reference from Intel: Intel-HD-Graphics-Driver_K86RM_WIN_27.20.100.8935_A07.EXE

https://downloadcenter.intel.com/product/126790/Intel-UHD-Graphics-630

INTEL-TA-00438 is not here: https://www.intel.com/content/www/us/en/security-center/default.html

Yep, very strange its needs to be kept secret!

There is a link on that page to:

https://www.intel.com/content/www/us/en/security-center/advisory/intel-sa-00438.html

SA-00438 is about an Elevation of Privilege flaw in Intel Graphics drivers that would require an urgent patch.