Microsoft says that computers with Realtek or Qualcomm Bluetooth radios might have issues after installing or updating to Windows 10 version 1903 because of outdated drivers. Microsoft also added a Windows 10 May 2019 Update block to make sure that none of the affected computers can be updated to the latest Windows version which is not compatible with out-of-date Realtek and Qualcomm Bluetooth drivers. Users can check with their device’s “manufacturer (OEM) to see if an updated driver is available and install it.”
Source: https://www.bleepingcomputer.com/news/microsoft/windows-10-may-2019-update-blocked-by-old-bluetooth-drivers/