Retail Windows 10 Pro digital license won't move to new PC: "I changed hardware" troubleshooter doesn't list the old device (0xC004F213)

I moved from an old PC (MSI Z270, Intel) to a new one (Gigabyte B850, Ryzen 9 9950X) and cannot activate Windows 11 Pro there.

• The old PC runs Windows 10 Pro, RETAIL channel, permanently activated. Its Activation page says "activated with a digital license linked to your Microsoft account".
• The old PC appears under my account's devices at account.microsoft.com.
• The new PC has a fresh Windows 11 Pro install. I signed in to Windows itself with the same Microsoft account.
• Activation shows error 0xC004F213 ("no product key found"). slmgr reports license status 5 (notification), reason 0xC004F034.
• Settings → Activation → Troubleshoot → "I changed hardware on this device recently" lists no device.

Already checked: both editions are Pro, the activation servers are reachable on port 443, there is no proxy, and the clock is correct. The key stored on the old PC is the generic Pro key (VK7JG-…-3V66T). There is no OEM key in the firmware. Microsoft support says it is not available for personal accounts.

A similar thread (no fix there either): https://techcommunity.microsoft.com/discussions/windows11/windows-license-will-not-transfer-to-new-motherboard/4554117/replies/4554223

Why does the troubleshooter not list the old device, and how do I get the license moved without buying a new one?