Have I Asus; ~2 yr old laptop: keyboard periodically stops working:: WHY? I run Windows10...?

It's one of these reasons.

-Keyboard drivers need to be updated or rolled back to a more stable version. The Chipset drivers may also need to be updated.

-The keyboard is dying/malfunctioning.

-The small ribbon cable or port that connects the keyboard to the motherboard is damaged.

-The Chipset (Control Hub) is having issues.

I have a Lenovo Flex 3 and the keyboard will periodically stop working, but I can resolve the issue if I reboot the PC. I figure the main reason to be either the chipset drivers or the BIOS/Firmware. So, the main reason I'm having issues is Lenovo has done a poor job with the software/driver support for the Flex 3. However, I've also noticed that the issue is more prevalent with certain versions of Windows 10.... such as version 1709. The issue went away with version 1909 but it came back with version 20H2. The problem isn't so much Windows as it's Lenovo's ability to make sure their systems work smoothly with these various Windows updates. 

try the following:  1. update/replace the keyboard driver  2.  take it to a technician for hardware testing

take it to a computer place and let them fix it

Most likely malware.  It could also be a failing hard drive, if you have a mechanical hard drive.  While the keyboard is working, do ctrl/alt/del, launch task manager, click on performance tab.  If you see hard drive go to 100% and stay there a while, your hard drive is failing.  If you see CPU go above 50% and stay there a while, then that is probably malware.