If I'm using StoreKit 2 and App Store Server Notifications v2, do I really need to implement Transaction.updates inside my app? My app has an auto-renewable subscriptions InApp Purchase and I don't want to have data race problems with the subscriptions status updates on my server.
App Store Server Notifications and Transaction.updates
100% - that is how your app sees new transactions and handles revoked transactions. Server notifications are more for maintain status but you will still need client implementation to finish transactions so they are removed from the queue.