I appreciate your help. Actually I was getting the error due to some JS code ingestion browser extension that I was working on. Switching to another browser helps me.
https://trailhead.salesforce.com/trailblazer-community/feed/0D54V00007ZB9KYSA1
2番のType add and select the Add Prompt Instructions element to add to the flow.が機能しない
Please make sure you have enabled this flow