This seems badly broken. I can add a single OBFB account in OneDrive and can see that in Apple iOS Files app (after authenticating again)
If I add an additional ODFB account and then open the Files app, the first account is now gone and replaced by the second. The first account is my own 365 tenant, additional accounts are client tenants in which I have an account.
Seeing this behaviour across multiple iOS devices.
Have tried clearing accounts, cache etc
Anyone else tried this ?