For the use case where the servers are located in a single region, EU in this case, it is a valid approach to define a single regionBaseUrl.
To comply with the data residency requirements, you’ll need to ensure that all the in-scope data is stored within this region.
With data residency, customers who pin their app to a region will not lose access to your app.
Within the customer facing data residency UI, customers who have their product pinned in EU will currently see the app pinned in global. If you adopt the additional regionBaseUrl and the realm migration APIs, these customers can then align their app traffic to EU. After a new version of the app with the EU realm support has been released, any new installations on products in EU will automatically pin towards the EU URL; however other regions will point to your baseURL or global.
the idea behind the data residency feature is that both regionBaseUrl and dare-migration are required for it to be fully functional and to cover all the scenarios.
If the plan is to only support one region, you could omit both tags and provide the information about where the data is located in the privacy and security tab.
If the tags are not defined, in the initial version of the customer facing data residency UI, the app will be shown as “Not Eligible” for those customers who pinned their product to a location and customers will be guided to check the privacy and security tab of the Marketplace listing.