Hey @Skyhooker,
Go with whatever you’re comfortable with… as long as it can handle Linux permissions. So BTRFS is fine, but stick to the Ubuntu recommendation.
This should get you started on changing data directory How to manage external media and storage for Nextcloud snap but that comes with some caveats requiring careful configuration considering How to backup, restore and migrate Nextcloud snap.
Make sure you have Requirements covered and read Configuration, see FAQ’s if you get stuck.
Feel free to check out Nextcloud snap wiki and support and don’t hesitate to ask if something is unclear.
Also check out our Home · nextcloud-snap/nextcloud-snap Wiki · GitHub for more helpful information around Nextcloud snap