You can disable that in Cluster Management Console -> Settings -> Preferences under “Allow Dynatrace Support remote access to environment monitoring settings”. If that option is disabled contact with Dynatrace One via help chat or your sales rep.
What is the reason you want to opt-out? How can Dynatrace assure you to keep that enabled?
See my comment. Blocking that on network level is not the best solution as it is considered as misconfiguration by Dynatrace Mission Control team. If someone wants to opt - out - there is an option to do that in the product.
It is not recommended that you block out Dynatrace from your cluster nodes as they perform routine health checks and will alert you of any issues as well as take action to resolve issues on the back-end of your Dynatrace instance.