I am migrating from the legacy FCM cloud messaging API to the newer HTTP v1 for push notifications for my app. However in the new cloud manager for Pub/Sub I don't see any of the previously registered topics that were all setup when the legacy FCM was active.
Do the topics and subscriptions created from legacy FCM automatically exist in or migrate to the HTTP v1 api? Or do I have to recreate them all again?
If they exist, where can I find them?
Topics are auto-created when the first token subscribes to them, and (iirc) also when you first send a message to them. There is no different between topics in the legacy or the versioned API, they're literally the same.
Given your mention of "cloud manager for Pub/Sub", it sounds like you're looking for them in Google Cloud Pub/Sub. While that product also support subscription to topics, those topics have nothing to do with Firebase Cloud Messaging. These are separate products, each with their own set of topics.