As you know, you have been able to sign in with a personal account to Microsoft Teams running on iOS or Android devices for few months now (see https://t.co/ycs5PvlUYO)
Well, this capability is coming to Microsoft Teams too, in addition of a new account experience.
The new account experience (applicable to user which have been invited as guest to another organization) is simplifying the organization switch
In addition of this new account experience, you will be able to also sign in to Teams using your personal account as you have been able to do it on iOS or Android devices.
The process to add a personal account is similar to the one for Teams on iOS or Android.