Hi Albert Koppelmaa
Test with an external USB keyboard, ensure it is working well.
I would suggest you to change the whole keyboard module.
They can be found at ebay, amazon, etc
Just an example:
https://www.ebay.com/itm/NEW-UK-English-Keyboard-Lenovo-Yoga-710-15-710-14-710-14ISK-Flex-4-14/183147453227?hash=item2aa4705b2b%3Ag%3AVdUAAOSwISRaiQsc&_sop=15&_sacat=0&_nkw=+Lenovo+Yoga+710-14ISK+keyboard&_from=R40&rt=nc
Notes: Based on some models of lenovo I had worked with, I think to replace the keyboard, you need to remove the mainboard and battery to access.