Law and billing
Data residency and jurisdiction
Where data is physically stored is one question; whose law can reach it is another. The second one depends on the provider, not the rack.
Data residency is the requirement, from a law, a contract or a policy, that certain data stays within a country or region. Hosting it in a datacenter there satisfies the letter of that. The GDPR itself has no residency rule for the EU; it restricts transfers outside the EU and EEA.
Jurisdiction is the other question: which courts and authorities can order the provider to hand data over. That follows the provider's corporate chain, not the server's location. A company with a parent outside the EU is subject to that country's orders wherever the server stands; Article 32 of the EU Data Act asks providers to say so and to take measures against such access.
So when a procurement form asks where the data is, the full answer has three parts: the datacenter, the company that operates the systems and every sub-processor, and the law that governs the contract. A provider that can answer all three with one country and one company is the simple case.