I've had a request from a client which I thought would be simple however it is turning in to a nightmare.
It is to share calendar free/busy between two Office 365 tenants.
As a proof of concept I've added both domains in each others tenant and the Organization Sharing now shows my two 'federated' Exchange organizations listed.
However calendar information is still not showing between any users cross-tenant.
One of the clients is a hybrid environment with existing on-prem Exchange and one is cloud only.
I've also added each of the Domains in to the Default Sharing Policy in case this was being caused by calendar permissions.
I'm a bit stumped as what is causing this to fail and Microsoft do not seem to have much information on this except how to configure which is already done. I've seen blog posts where people have configured it in the same way as me and it is working.
One thought that I did have was; is any of this affected by conditional access as one of the clients have strict conditional access, but without knowing for sure I do not want to really touch these.