You will need to update to driver version or later to remove this safeguard hold. Microsoft’s response: To safeguard your update experience, we have applied a compatibility hold on devices with affected driver versions for Realtek Bluetooth radios from installing Windows 10, version 1909 or Windows 10, version 1903 until the driver has been updated. Please go to aka.ms/realtek_bt_1_5 to learn more.” Your PC has a driver or service that isn’t ready for this version of Windows 10. The following things need your attention to continue the installation and keep your Windows settings, personal files, and apps. Microsoft asks you to visit aka.ms/realtek_bt_1_5 to learn more.

The What needs your attention window will appear and point out the problem.

Some compatibility issues have been discovered by Microsoft for instance, some driver versions for Bluetooth radios made by Realtek are not compatible with the new versions of Windows 10. Can’t Update Windows 10 due to Old Realtek Bluetooth Drivers

Realtek bluetooth driver