Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
Hi,
To assist you with the issue, the error message indicates that your Universal C Runtime (CRT) in Windows 8.1 is not up-to-date. You can download the update on this link. If you are using the same operating system with the same product key, you can still go back to Windows 10. But if you have a different product key for your Windows 8.1, you can still install Windows 10 but you need to pay for the new product key. To know more about digital licensing, you can view it here.
Let us know how it goes.