I recently passed the Cisco 700-821 IOTSE exam and wanted to share how I prepared. The exam is 60 minutes long and covers four areas: Cisco Industrial Ethernet Switching (30%), Cisco Industrial Wireless (20%), Cisco Industrial Routing (25%), and Cisco IoT Operations Dashboard (25%). I took the topic list and weights from Cisco's official exam description PDF, then looked for a resource that was organized the same way. I chose ITExamsTopics because its content is arranged topic by topic, which matched the blueprint closely.
Before paying for anything, I tried the free practice test that comes after the topic, and it was good enough that I took the subscription. I prepared with it, and when I sat the exam I passed without much trouble. If you are planning to take 700-821, feel free to ask me anything about my preparation approach and I will gladly help.