Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
Hello firefinder,
Welcome to Microsoft Community.
I am a Microsoft user just like you, I hope you are doing well?
If you have Office 2021 product key, you can redeem this product key to your Microsoft account and install at anytime. It is a lifetime license so it will be available in your Microsoft account services and subscription page.
To redeem the Office product key:
Step 1: Go to www.office.com/setup or Microsoft365.com/setup.
Step 2: Sign in with your Microsoft account, or create one if you don't have one.
Step 3: Enter your product key, without hyphens, if prompted.
Step 4: Follow the prompts to finish the redemption process.
Once you have redeemed the product key to your Microsoft account, you can then install Office by signing in https://office.com/myaccount on your new PC oncdme purchased.
Source: https://support.microsoft.com/office/0a82e5ae-739e-4b92-a6f4-2ec780c185db
Please let me know if you need more assistance.
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Warm Regards