Which of the following queries is not supported in PushTopics?

The choice indicating that queries with relationships are not supported in PushTopics is accurate. PushTopics in Salesforce are designed to work with simple queries that track changes to specific records. They utilize a simplified query language aimed at monitoring changes to individual Salesforce objects rather than handling complex relationships, which involve multiple objects and require joins. This limitation ensures that the notifications sent through PushTopics remain lightweight and focused solely on the changes relevant to the specified object.

Queries involving IDs, simple queries, and those with multiple fields are all permitted in PushTopics. The ID-based queries can directly reference specific records, while simple queries can focus on single objects, and queries with multiple fields allow for monitoring changes across various fields of a single object. These features make PushTopics a powerful tool for real-time updates while keeping the operations efficient and straightforward.