How do i get my music player to see the music on my external SD card?

I have a Pixel 2xl. I have tried 3 different devices in the usb-c port that claim to be able to play music and videos directly from them but I can't get any music or video player to do so. If I access it with a file manager, the files are there and will play if I select one. But the apps themselves will not show the files. What gives? My Pixel does not have an SD card slot so how else can I get to it?

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