My "radio" is shown attached below. It has the Google Assistant built-in, but it is now disabled because it won't function unless I subscribe to a service in my owned car.
I have all my music in mp3 format.
The stick is the one I linked previously.
The stick is plugged in to the USB-C port under the climate controls.
The stick is file format NTFS.
If the stick is unplugged, it can take the system quite some time to recognize it once I've plugged the stick back in.
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Issues with using a USB stick for music in these "premium" cars:
There is no way to search/play a specific song via voice command (from the stick).
If two songs have the same title, only 1 of them will ever play, despite the songs being in distinct folders.
I have about 3,000 songs on the stick. The manual scrolling locks up after a few hundred.