The smartphone is designed to do everything well, but it's no substitute for an excellent audio player, an excellent camera or a very powerful computer. They have to make compromises to pack everything into a compact package at a 'decent' level of quality and price. You could draw a comparison with cars: a mid-range SUV does everything right, while a Ferrari is optimised to do just one thing perfectly :)
Unfortunately, we do not have any personal user experience with this product, but I am happy to forward your question to the Community, perhaps a Community member can help you.
The FiiO JM21 is not displayed in the Finder under macOS Catalina 10.15.7 because the Mac system does not support the MTP protocol. To access the files anyway, you must install the free "Android File Transfer" app.
Quick guide:
Download Android File Transfer and install the app.
Connect the JM21 to the Mac via USB-C.
Open the app - the memory is displayed.
The device does not appear in the Finder itself, this is normal. For pure music playback on the Mac, you can use the USB-DAC mode.
The iTunes library cannot be downloaded directly to the player, as Apple Music and iTunes files are often DRM-protected and are in a format that is not directly supported by the player.
To transfer music from the iTunes library to the player, you must first convert the music files to a compatible format (e.g. MP3, AAC, FLAC) that does not have DRM restrictions. To do this, you can use special software such as the ViWizard Apple Music Converter, which converts Apple Music songs into lossless formats and removes DRM. After conversion, you can then transfer the files to the player via USB and play them locally.
The player supports local music playback and can be connected to the computer via USB to transfer files. However, direct synchronisation with iTunes or Apple Music is not possible.
There is only one way to connect a FiiO JM21 to any amplifier.
For example, use the Fiio LR-3.5A audio cable ( art Galaxus 43488541 ) and you will be able to
listen to "recorded" or "streaming" music (e.g. Qobuz) from your JM21 on your amp.
The other option is in USB DAC mode on a computer and it then works like a sound card.
Apart from these 2 options, there are no other possibilities for the JM21.
DACs are headphone amplifiers.
DACs are designed to transform a digital signal coming from a computer
into an analogue signal.
The FiiO JM21 runs on Android and allows the installation of third-party apps such as Podcast.de. However, the Sony NW-E394 is described as easier to use.