Move Windows 10 Digital License

I just cleaned and reinstalled Windows 10 on my old PC. Getting it ready to sell.

It was a retail Windows 7 key that became a digital license when used for 10. It automatically reactivated on install.

It is a full Windows 10 Pro Retail license so I want to keep it for later use.

You can deactivate it but there is no way to see a digital license for a future install.

All the help forums say to deactivate and re-enter the key but you can no longer see the key.

I think that these articles should be able to help you:

How to transfer a Windows 10 license to a new PC or hard drive | Windows Central

Use Activation Troubleshooter in Windows 10

Every article I have read somehow assumes you can still see the key to be able to re-enter it on another computer.
I started with an actual Windows 7 key to activate 10. At that point it became a digital license and you can no longer see the new key.

It did reactivate automatically on reinstall.

When I go here it shows nothing.
account.microsoft.com/devices

If I deactivate it I have no idea if I will be able to install on another PC without an actual physical key.

Take a look at the second article that I linked to regarding the use of the activation troubleshooter.

You will want to make sure that the old system is associated with your Microsoft account first so that you can then select that system when using the activation troubleshooter to tell it that you have changed hardware. You should be able to tell the troubleshooter which machine the previously licensed system was.

I've done this successfully in the past myself, but it has been a few years

Make sure you log into the old activated computer with a MS Account. That will allow you to copy the digital license with the activation troubleshooter on the new computer. You have to be logged into the same MS Account on the new computer.