It will work with Steam, as Steam itself is able to capture Switch-input, but if you try to use it outside of Steam in a software that expects X-Input it will not work as expected.
I wasn’t able to use it on Android in BT mode either, most games I tried wouldn’t recognize it, but would work fine using a USB-C cable.
There’s a difference between the Ultimate BT (with hall effect joysticks and the paddles) vs the Ultimate 2.4g, which received BT support later on. They don’t use the same firmware.
The Bluetooth mode is made specifically for the Nintendo Switch on that model, on PC and Android you need X-Input mode, which is made available through 2.4GHz and USB-C.
I complained about that part too, and 8bitdo doesn’t seem receptive…