NextCloudPi on Pi, Data on Synology NAS - Fail

Hi all,
I’ve been playing around with NextCloudPi on my Raspberry Pi for the last couple of weeks.
Everything works like a charm: installation, ddns, let’s encrypt, personalisation, apps, file sharing,…
I’m not a Linux command line pro, but it’s also not the first time I toy around with it and I encountered zero problems. Thanks for that @nachoparker, incredible work!

Since having this cloud tool working off a SD card is not a long term option, I would like my setup to be:

  • only NCP instance running on RPI
  • DataDir + db on Synology NAS (which has a live physical mirror in a second location + a nightly cloud backup)

My Synology is formatted in BTRFS. I created a new share for NC, made it available over NFS and used squash no mapping so it’s R/W for every user.

On the Pi, I mount the NAS at boot with fstab over NFS, I modified owners and permissions for the dir.
In command line on the Pi I can access the share and read, write, delete files on the mounted folder.

When I log into NCP Panel and use the nc-datadir to move the data to the mounted folder (/media/ncdata), I get this error:
[ nc-datadir ]
Only ext/btrfs filesystems can hold the data directory

This error happens with existing installation and fresh one.

What am I missing?