Upon trying to launch any realm or world created before 1.16.101 the game shortly crashes after loading the realm. I've narrowed this down to what appears to be an issue with either the version just crashing due to a random bug or to somehow deal with Microsoft's cross platform SSO system. 

I purposely kept my iPad a version back to test this out and the iPad running the previous version worked. 

I then updated without signing in to MS and played an old world on the new update 1.16.101 

I then signed in and would encounter a crash every time. 

all deceives were running iOS 14.2