Doc section:

1.5.5.1.3.3. Optional: Configuring the klusterlet to run on specific nodes

Doc link:

https://access.redhat.com/documentation/en-us/red_hat_advanced_cluster_management_for_kubernetes/2.9/html-single/clusters/index#import-configuring-nodeselector-tolerations

What to fix:

The YAML switch that the doc talks about on the cluster page does not exist.
To be able to add these annotation on the managed cluster you will either need to edit the managedcluster resource using ACM search feature or use oc cli to edit the managedclusters