In my 2017 Tiguan SEL (MIB2) I had all my music on a 64gb SD card in the glovebox. Mixture of MP3s and 256kbps AAC from iTunes, with some .M3U playlists. All worked fine.
My 2020 Tiguan Elegance has the new MIB3 system, which just has the two USB-C ports in front of the gear selector. At first I tried the original SD card using a USB-C to USB-A adapter and a sandisk card reader, which worked fine but looked rubbish. Most USB-C flash drives are a bit longer than 'standard' USB ones as the smaller plug size means you can't fit any circuitry inside the plug itself. The neatest solution I could find was to buy a small USB C to A adapter and I already had a tiny 64gb Sandisk USB 3.0 flash drive as follows:

https://www.amazon.co.uk/nonda-Adapter- ... 173&sr=8-3

https://www.amazon.co.uk/SanDisk-Ultra- ... 4119696677
At first it was really slow and buggy, taking ages to browse, tracks randomly pausing and just general instability. I tried another USB adapter to no avail. Then I reformatted my USB stick from FAT32 to exFAT and now it works perfectly. Turns out my original SD card was already formatted to exFAT.
The only annoying thing vs old version is that it seems to keep forgetting what it was last playing, so when I restart the car to drive home, it plays the first track on the USB stick. Anyone know a way around that?
Lastly, can confirm that with MIB3 you finally get the time displayed on the driver's AID.