Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Perpetual licenses usually allow for one activation only, which means that moving from one computer to another could cause trouble.
Getting in touch with Microsoft support may be required to get the new install activated. Try using the phone number for your region from the article at https://support.microsoft.com/en-us/office/-telephone-activation-is-no-longer-supported-for-your-product-error-when-activating-office-9b016cd2-0811-4cb3-b896-5a6a13177713 . The idea is that you stay on the line until a real person responds (bypass all the automated prompts).