Preorders open on 8th April.

The US site lists May 8. Preorders also seem to be invite-only in the beginning?

From the US site:

Invitation emails will be prioritized on a first-come, first-served basis to registrants who have purchased a Nintendo Switch Online membership with a minimum of 12 months of paid membership and a minimum of 50 total gameplay hours, as of April 2, 2025. Once invitation emails have been sent to all registrants meeting the priority criteria, invitations will be sent to remaining eligible registrants on a first-come, first-served basis.

The German site lists April 8, but requires you two have a Nintendo online subscription for the last two years.