1.18 > 1.20 upgrade, certificate signed by unknown authority

I upgraded my server from 1.18 to 1.20 using the upgrade script and the server log now repeats the following certificate error:

Jan 30 09:46:26 qotom k3s[29291]: E0130 09:46:26.045097   29291 authentication.go:53] Unable to authenticate the request due to an error: [x509: certificate signed by unknown authority, verifying certificate SN=<nnnn>, SKID

In the upgrade process from 1.18 to 1.20 was I supposed to do more than just run the install script as shown in the k3s upgrade page. I now see that the kuberetes kubeadm upgrade steps follow a much more detailed process.