I tested BluetoothAdapter adapter = await BluetoothAdapter.GetDefaultAsync();
and found out that IsPeripheralRoleSupported = false.
I tested on both desktop and laptop, which are both Windows10(1903), but had no luck.
Is there any way I can enable the PC to support peripheral role?
Or is this property unable to be changed?
Mike Petrichenko answered on the comment if anyone looking for the answer to this question!
You can but with very few Bluetooth Adapters. 100% working one is Laird BT851
You can not "enable" it. It depends only on hardware (Bluetooth module). Use compatible Bluetooth module (the one I posted above is compatible) and GATT server (peripheral mode) will work. Windows has very special requirements fro Bluetooth hardware to support peripheral mode and only few devices can be used.
It's a dongle (https://www.digikey.com/product-detail/en/laird-wireless-thermal-systems/BT851/BT851-ND/8251358). You should replace your one with this. Or, if you have build-in dongle, disable build-in. There are also 2 more known and tested models but they are not USB.