If you previously had a different Bluetooth dongle (or an old 4.0 adapter), the old drivers can conflict with the new UGREEN 5.3 driver. It is highly recommended to uninstall old Bluetooth software before plugging in the new UGREEN adapter.
Microsoft's generic driver often limits the adapter to Bluetooth 5.0 features (2 Mbps PHY, LE Advertising Extensions) unless a dedicated vendor INF file unlocks 5.3 features (LE Audio, LC3 codec, Periodic Advertising). This is why UGreen provides a "driver download" on their site – it's actually a custom INF + Realtek firmware loader that tells Windows: "This device supports the full 5.3 feature set." driver ugreen bluetooth 53
The adapter is primarily designed for Windows 8.1/10/11. If you previously had a different Bluetooth dongle