An easy check if you have a spare keyboard. Have you tried an external keyboard? If there isn't an issue then likely it is your keyboard.
Not an easy test but if you really think it is the OS upgrade then go back to the old OS and see if it still is a problem. Generally when we see a "this happened with the latest update" posted here the timing is purely coincidental.
If you think it is the OS, tell Apple about it Product Feedback - Apple
Go to this page to find your nearest Apple Authorized Service Provider (AASP) or Apple Authorized Distributor (AAD) --> Find Locations
How to make a Genius Bar appointment
1. Go to Genius Bar Reservation and Apple Support Options - Apple
2. Go to "Get hardware help".
3. Select your hardware and continue selecting options requiring replacing parts until you see "Bring in for Repair"
4. Sign in with your Apple ID
or:
Refer to this document for ways to contact Apple ➞ Choose your country or region - Official Apple Support
Select your country (also look for "other" regions), then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
Contact Apple for support and service by telephone ➞ Contact Apple Support - Apple Support
