Same problem here (looks like other tickets as well like REALMS-13059), it started with the happy ghast update. With 1 player in the realm on the Nintendo Switch it’s fine, let’s say the player is “Jon”, then when another person on tries to join on a second controller with the + button they can choose their Nintendo profile (which has a different Microsoft account linked) but when it loads no matter who they picked it makes the person “Jon (1)”. That second person is like a brand new profile at spawn so there is no way to continue playing with 2 people on the switch on Realms currently.
Same problem here (looks like other tickets as well like REALMS-13059), it started with the happy ghast update. With 1 player in the realm on the Nintendo Switch it’s fine, let’s say the player is “Jon”, then when another person on tries to join on a second controller with the + button they can choose their Nintendo profile (which has a different Microsoft account linked) but when it loads no matter who they picked it makes the person “Jon (1)”. That second person is like a brand new profile at spawn so there is no way to continue playing with 2 people on the switch on Realms currently.