Having a way for you to know a cluster update is available is something we should work on, (cc @Alessandro_carrano), there is no way for you for the time being to know if a new version is available.
There is no diff / changelog on what will be applied on your cluster for the time being, it should be considered as daily routine.
But out of curiosity, what would you like to know on that front? Given the fact your cluster is fully managed, do you want to know what changes?
You will have a badge saying you should update your cluster if you change any settings on it (advanced settings, node type, etc), but that’s it for now.
Our cluster updates are meant not to be breaking nor cause any downtimes and can be run anytime without causing services interruptions.
If we need to proceed with updates leading to downtime eventually, we are extra cautious and communicate ahead (for example for kubernetes updates).
Cheers