Microsoft today announced that they managed to resolve the upgrade blocking issue for Windows 10 version 1909 and some older releases of the OS causes by the Realtek Bluetooth Radio driver.
If your Windows 10 PC has an outdated Realtek Bluetooth Radio driver, it will give you upgrade issues if you try to install Windows 10 version 1909. According to Microsoft, devices with Realtek Bluetooth Radio drivers older than version 1.5.1012 are affected.
Microsoft had set a compatibility hold on such devices, but has removed it as of now. The updated list of known issues states:
Resolution: This issue was resolved with an updated driver for the affected Realtek Bluetooth radio and the safeguard hold has been removed. Please note, it can take up to 48 hours before you can update to offered Windows 10, version 1909 or Windows 10, version 1903.
So, affected devices should receive a new version of the driver automatically and then offered to install Windows 10, version 1909 or 1903.