Hi @eg1995
Yes, Exchange online retention policies can be applied to tenant wide for business premium.
Here is a thread discussed the similar question as yours, you could take a reference: Business Premium - Retention Policies
Please Note: Since the web site is not hosted by Microsoft, the link may change without notice. Microsoft does not guarantee the accuracy of this information.
And for eDiscovery:
If an Answer is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.