I have found this: https://answers.microsoft.com/en-us/windows/forum/windows_10-windows_store/error-code-0x80073d26-cant-install-gaming-services/ca90a836-f369-40c8-8b51-b18369795bab?auth=1
It works, but requires Windows registry editing which can seem a bit daunting if you've never done it. Take your time, go slowly, not too difficult. Fix has been working ever since I did it.
Regards