This is an old fix and extremely simple, so I'll keep it short and sweet...
This issue popped up on my Wife's laptop a little over 2 years ago now.
The only keys that worked were in the diagonal plane following the pattern:
1 Down, 4 Down, 5 Down, 9 Down, and 0 Down
To fix, hold the power button down for 30 seconds to do a hard shutdown.
You can see my original post on Reddit, and the dozen+ comments of people replying saying it worked for them as well: https://www.reddit.com/r/techsupport/comments/mddcwq/help_with_keyboard_not_working_on_lenovo_ideapad/gv44u3w/