Microsoft will be making changes to account sign-in, from February if you sign into Microsoft services it will keep users logged in automatically. There is a new global sign out option called "sign out everywhere" if you forget to sign out on a computer you don't own. This may take up to 24 hours for Microsoft to sign you out of all your devices. That means there is still 24 hour window in which others can still access Microsoft account and any other related services you have signed into. The change affects all Microsoft services, including Microsoft 365, Outlook, OneDrive and other services and products that support login this method of sign in. So its important you sign out of your account.