Sadly, I've confirmed with Ubisoft Support that Ubisoft Club does not support linking Nintendo Switch to your existing Ubisoft Club or the ability to create a new account for Switch yet. So even when using your correctly entered Ubisoft Club login that's why it doesn't allow you to log in or create a new account...thus leaving Trails Rising Online Multiplayer unavailable until they choose to add it for Switch. Maybe 6 months or a year from now it'll be added, who knows?

Would have been nice to know that prior to buying the Switch version, Ubisoft! I've heard of some ridiculous work arounds to get it working, but Im not adding a Japanse profile to my Switch lol.

If anyone knows more, I'd love to hear, thanks!