Thank you for reaching us!
I understand that you would like to deactivate 2fa for a single account to use the multiple users.
If your tenant is enabled the Security defaults it is applied to entire tenant and it is indeed not possible to exclude the one account.
If you are using per-user MFA in tenant you can disable or enable for individual user, but this feature is going to deprecated
If you are using conditional access policy, you can exclude the user from the policy to skip the MFA.
If your tenant is demo or not applied the security defaults or conditional access policy Microsoft made Mandating multifactor authentication (MFA) for your partner tenant.
Hope this helps. Do let us know if you any further queries.
Thanks,
Akhilesh.
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