Where did you add the link for the External Storage section?
Also, i would like to short the section by removing the part where you say that exFAt is not supported.
Let’s include the exfat driver on the SD and that’s all 
Could you try to install the driver and test if it works automatically?
apt-get -y install exfat-utils
Thanks!
Lemme grab a spare drive and test that!
And I linked it from both https://wiki.zynthian.org/index.php/Zynthian_UI_Users_Guide and https://wiki.zynthian.org/index.php/Zynthian_Features. As well, to ensure search coverage, I created a redirect “USB drive” that points to “External storage”.
Edit:
Nope, just installing exfat-utils doesn’t let automount see it. Audio record goes to SDC, and the drive is not visible in du:
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/root 29950364 9895632 18706708 35% /
devtmpfs 4045056 0 4045056 0% /dev
tmpfs 4078848 80508 3998340 2% /dev/shm
tmpfs 4078848 8620 4070228 1% /run
tmpfs 5120 4 5116 1% /run/lock
tmpfs 4078848 0 4078848 0% /sys/fs/cgroup
/dev/mmcblk0p1 258095 54407 203688 22% /boot
tmpfs 815768 0 815768 0% /run/user/0
Looks like it’s just automount, though, nothing deeper, because if I manually mount it and /media/usb0, Audio Recorder uses it just fine.
root@zynthian:~# mount -t exfat /dev/sda1 /media/usb0/
FUSE exfat 1.3.0
root@zynthian:~# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/root 29G 9.5G 18G 35% /
devtmpfs 3.9G 0 3.9G 0% /dev
tmpfs 3.9G 79M 3.9G 2% /dev/shm
tmpfs 3.9G 8.5M 3.9G 1% /run
tmpfs 5.0M 4.0K 5.0M 1% /run/lock
tmpfs 3.9G 0 3.9G 0% /sys/fs/cgroup
/dev/mmcblk0p1 253M 54M 199M 22% /boot
tmpfs 797M 0 797M 0% /run/user/0
/dev/sda1 7.6G 4.7M 7.6G 1% /media/usb0
I think the issue may be that exfat is a FUSE filesystem, which requires special handling in udev. Possibly we could grab the kernelmode driver for exfat instead? Though that would be outside vanilla raspbian because of licensing concerns, I believe. I’ve not looked at the Samsung code, but I know several linux distros are going FUSE on exfat for licensing reasons/fear of Microsoft.
Same experience here with a new exfat usb disk, after install exfat-uitils the drive didn’t show up, but mounting manually did the trick.
Obviously this is not a sustainable solution, so hopefully this can be improved. If possible, I’d rather not reformat the USB disk. (The same USB disk is automatically mounted perfectly on another linux system)