Graph API access to Exchange Server 2019 hybrid setup (on prem mailbox)

I read within the Microsoft docs (https://docs.microsoft.com/en-us/graph/hybrid-rest-support) that it should be possible to access basic resources like calendar or mail via the Graph API.

Behind the scenes, when Microsoft Graph identifies that a REST API call is attempting to access an on-premises mailbox in a hybrid deployment, it proxies the REST request to an on-premises REST endpoint which then processes the request. This discovery makes accessing the REST API possible.

We are using a hybrid setup with Exchange Server 2019 and on Prem mailboxes, but unfortunately I'm not able to access any data from there via Graph API.