I've been using it for a few weeks: It doesn't force you to put anything on the cloud. If you choose to create an /e/ account, it makes it easy to sync/backup to their cloud services, but it's completely optional.
Unlike Google or Apple, you're not required to create a cloud account just to use your own device.
The cloud "just" uses davx5, which you can ignore, or use to sync to your own nextcloud server, or you can create an account on their nextcloud instance.
I obviously use my own nextcloud.
Some mircrog stuff is enabled by default, which means it does allow apps to talk to Google for eg. push messages. It's not much work to disable, though.
Does it force you to have data on the cloud? Or can you get by without using the cloud?
Simply put: I don't want anyone having my data anywhere apart from me and my device.