@Laurent Knafo
I'm glad that you were able to resolve your issue and thank you for posting your solution so that others experiencing the same thing can easily reference this! Since the Microsoft Q&A community has a policy that "The question author cannot accept their own answer. They can only accept answers by others", I'll repost your solution in case you'd like to "Accept" the answer.
Issue:
When trying to delete your old Azure AD tenant following our Delete a tenant in Azure Active Directory documentation, and after following the Remove enterprise apps that you can't delete section, you weren't able to login to the Azure Portal and received the AADSTS7000112: Application '.....974e53cbdf3c'(Azure Portal) is disabled
error message.
Solution:
After many unsuccessful attempts Get-MsolServicePrincipal -AppPrincipalId ....974e53cbdf3c | Set-MsolServicePrincipal -AccountEnabled $true
, finally succeeded and you're able to login into the Azure portal.
Thank you again for your time and patience throughout this issue!
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Please remember to "Accept Answer" if any answer/reply helped, so that others in the community facing similar issues can easily find the solution.