As you know, there is a GREAT CHANCE TO LOSE FILES at local PC if something goes wrong with the syncing. At my company we stopped the nexcloud project after my boss lost 10GB of information because this behavior.
One way sync shold be a feature that allows to define which one between the server and the client would be the master or the slave, or to maintain strict sync. being the master role for the client the default.
We love Nextcloud but we’ll only start using it again the day it GUARANTEE local files will NEVER be deleted again.
My understanding is Nextcloud normally does not keep backups of the files by design… it just syncs them. I’d also love to see more robust sync options for users how want to prevent deletion… fyi, you might want to look into “locking” files… I’m sure other users can provide better info to you.
Check out rclone, which can make one way sync of your Nextcloud files to another location via webdav protocol.
There is also the Version Control app to keep past versions of a changed file. I haven’t tested it yet, so not sure how it handles deleted files.