Hi @Tanmay Mohanty,
Thank you for posting your question in the Microsoft Q&A forum.
Based on what you shared, and from what I could gather during my research, the error “Your installation cannot be activated because you have activated up to the limit of your Multiple Activation Key” indicates that your Office 2021 LTSC Standard installation is using a Multiple Activation Key (MAK) that has already reached its activation limit. Each activation (including reinstalling Windows or reinstalling Office on the same device) counts toward that total, and the limit is determined by your organization’s volume licensing agreement.
To better understand your situation and guide you appropriately, may I ask where you obtained your Office 2021 LTSC Standard license?
If you are part of an organization, do you have access to the IT admin who manages your volume licenses, or are you using this as an end user? The next steps can be quite different depending on your role and where the license originated.
When you get a chance, please reply under this post with a bit more detail, that will help me provide the most suitable guidance for your specific scenario.
Thank you for your time, and I look forward to helping you further.
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