The Azure DevOps Aggregator project allows you to write simple scripts that get triggered when a work item is created or updated. It uses a service hook to trigger when such an event occurs and abstracts most of the API specific stuff away, providing you with an instance of the work item to directly interact with.
You can't block the creation or update from, such a policy, Azure DevOps will inform the aggregator too late in the creation process to do so, but you can revert changes, close the work item etc. There are also a few utility functions to send email.
You need to install the aggregator somewhere, it can be hosted in Azure Functions and we provide a docker container you can spin up anywhere you want. Then link it to Azure DevOps using a PAT token with sufficient permissions and write your first policy.
A few sample rules can be found in the aggregator docs.
store.DeleteWorkItem(self);
should put the work item in the Recycle Bin in Azure DevOps. You can create a code snippet around it that checks the creator of the work item (self.CreatedBy.Id) against a list of known bad identities.
Be mindful that when Azure DevOps creates a new work item the Created and Updated event may fire in rapid succession (this is caused by the mechanism that sets the backlog order on work items), so you may need to find a way to detect what metadata tells you a work item should be deleted. I generally check for a low Revision number (like, < 5) and the last few revisions didn't change any field other than Backlog Priority.