Same issue. Completely uninstalled the game from the Switch (including wiping cloud saves and local save data), redownloaded, and logged into MS account. After doing this, so long as I don't do literally anything else, I can join a friend's realm. Going into the marketplace or a realm and backing out is apparently a no-no (crashes), and if I play too long, it will still eventually crash. Were this not happening on my friends devices, I'd suspect it was somehow just me, but this is definitely reproducible without much effort on other devices.
Donovan Wolf
Same issue. Completely uninstalled the game from the Switch (including wiping cloud saves and local save data), redownloaded, and logged into MS account. After doing this, so long as I don't do literally anything else, I can join a friend's realm. Going into the marketplace or a realm and backing out is apparently a no-no (crashes), and if I play too long, it will still eventually crash. Were this not happening on my friends devices, I'd suspect it was somehow just me, but this is definitely reproducible without much effort on other devices.