Hello drinkwaterj,
Welcome to Apple Support Communities!
We understand that your notes are not syncing between your Apple devices after updating the iOS recently. We'd be happy to help.
Is your iPad also updated to the recent iPadOS version?
Do you store your notes on a different account, not in iCloud? Like a third-party email account?
Are you missing notes or are they just not updating across devices? If you're missing notes, take a look at If you're missing notes on your iPhone, iPad, or iPod touch.
Lastly, are your devices connected to a Wi-Fi network or using cellular data? Ensure all are connected, maybe try resetting the connection as well.
Take care.