Hello, Charis chairs.
If you purchased the full offline version electronically (ESD), then the unique product key must be in the E-mail that was sent after paying for the license. The so-called "digital license linked to an account" is misleading for many users. That's what they called it (not very correctly) the fact that the license is linked to the PC, and the PC itself (the licensed PC) is linked to the Microsoft account. It's just for information...
Yes, after changing the processor or updating the BIOS, activation often crashes and it is not possible to restore it yourself. In this case, you should contact a Microsoft support specialist directly in the chat. To do this, log in to your personal account on the page https://support.microsoft.com/en-US/home/contact?SourceApp=smc2&ContactUsExperienceEntryPointAssetId=www.microsoft.com
In the search bar, type (without quotes) "agent support" and press Enter or click on Get Help. Ignore the search results, and click on the "Contact Support" button at the bottom. On the next page, select "Windows" and "Technical Support" from the drop-down lists, and then click on "Confirm". Next, select the chat "Chat with a support agent in your web browser" and on the next page, enter (if requested) your email address and click on "Confirm". A chat window will open in a new tab. Wait for the specialist's response and describe your problem. After checking the license on your PC, activation will be restored (if everything is in order with the license).