Using external storage, but deleted files are written to nextcloud directory on boot drive

I’m using a 4tb raid for external storage, and I’ve had a few “no disk space on boot” problems when my boot drive got filled with mystery files. I figured out early on that deleting files on the 4tb external was making the nextcloud data folder swell up. So I got in the habit of emptying all the trashes after I deleted any files. But sometimes I’d forget, and wake up in the morning to “no disk space…”

My company does graphic design, and we create a lot of files, and some extremely large (multi-terabyte) ones. That’s why this is a bigger issue for me than probably for most people.

After sizing up the boot drive from a 500gb to a 1tb, and again to a 2tb, I finally figured out what was happening: When files are deleted off the 4tb, they go to the nextcloud>data>user folder for the person that deleted them.

I came across a post somewhere in the Community here that suggested that’s the normal behavior, to stash them there either until they are trashed or verified as completely synced? Can someone confirm this? I’ve searched the web and the NC documentation and not found anything to answer my question.

I feel like now that I have a larger boot drive, this isn’t an issue anymore. But I’d sure like to hear someone explain how the whole system works and why.

I should point out that 10 months ago I was a total noob. I’m comfortable with all things Mac, but I had no experience at all with Linux, let alone Nextcloud. I’ve had a number of serious problems with both over that time, but I’ve been able to figure them out and become quite comfortable with my setup.

My info, in case that might help:
Beelink mini PC SEI12 with Core i5, 2tb nvme and 16gb ram.
4tb external ssd raid
Ubuntu 22.04.3
Nextcloud Hub 6: 27.1.0, installed in /var/www/nextcloud

Thanks for reading, and hopefully dropping some knowledge on my head.