Microsoft has now updated the Windows 10 update page to indicate if a device is now eligible to receive the update. If you plan to update your system to May 2020 Update and Microsoft has blocked the update, you will see the following message:
The Windows 10 May 2020 Update is on its way. We’re offering this update to compatible devices, but your device isn’t quite ready for it. Once your device is ready, you’ll see the update available on this page. There’s nothing you need to do at this time.
This is Microsoft’s way of ensuring that users know that their systems are currently unsupported probably due to one of the known issues or hardware incompatibility. This will also ensure that users don’t use other tools like ISO or Media Creation Tool to get around the block as that can cause issues like BSOD.