HawkOpen is made by TriStiX S.L., a company in Spain. The public privacy page does not name the hosting region yet; it says the final list of providers, the hosting region and the transfer safeguards will be published before the production services are switched on.
If the hosting location matters for your contracts, read the draft DPA in the app before you connect a mailbox, and wait for the final version if you need a confirmed one.