@Richard Berry, Thanks for posting in Q&A.
Based as i know, Global Admins have almost unlimited access to your organization's settings and most of its data. Multi-factor authentication is a process in which users are prompted during the sign-in process for an additional form of identification, such as a code on their cellphone or a fingerprint scan. Here is a link with more details:
https://learn.microsoft.com/en-us/azure/active-directory/authentication/concept-mfa-howitworks
On my point of view, if the global account Account 1 is used by one person, you can enable MFA to secure it. If it is shared by many people. maybe you can exclude it from the conditional access policy which require MFA.
As this belongs to Azure AD, to help you get professional support, I have added "Azure Active Directory" tag for you.
Hope it can help.
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