There are no "Windows 11 keys" yet because WIN11 hasn't been released yet AND the upgrade is free if you already have Windows 10 installed. You are probably selling  Windows 10 keys in order to get the free upgrade from those which will work IF YOUR COMPUTER IS COMPATIBLE with WIN11.

From Microsoft:
If your existing Windows 10 PC is running the most current version of Windows 10 and meets the minimum hardware specifications it will be able to upgrade to Windows 11. The upgrade rollout plan is still being finalized, but for most devices already in use today, we expect it to be ready sometime in early 2022. Not all Windows 10 PCs that are eligible to upgrade to Windows 11 will be offered to upgrade at the same time. To see if your PC is eligible to upgrade, download and run the PC Health Check app. Once the upgrade rollout has started, you can check if it is ready for your device by going to Settings/Windows Updates.
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Microsoft is announcing that Windows 11 will be released on October 5th. The new operating system will be available as a free upgrade for eligible Windows 10 PCs, or on new hardware that ships with Windows 11 pre-loaded.

The free upgrade to Windows 11 will start rolling out on October 5th, but like many Windows upgrades in the past, it will be available in phases. New eligible devices will be offered the upgrade first, and then Windows 11 will become available for more in-market devices in the weeks and months following October 5th.