There is no account here, so there is nothing for us to sync. That is the whole design, and it has a cost: getting your work onto a second machine is your job, not ours. This page says exactly how to do it, and is honest about the one approach people ask for most, which does not work and cannot be made to.
Put the folder you connected on the home page inside a folder that something else already syncs. Nextcloud, Syncthing, Dropbox, iCloud Drive, OneDrive, a network share, an encrypted volume on a stick: it does not matter which, because as far as this site is concerned the folder is just a folder on a disk. Everything you do here is written into it as an ordinary file the moment it changes, and whatever you use to sync picks it up from there.
On the second machine, open the home page, press the folder button, and point it at the same folder. From then on both machines are writing into the same place.
It gets you the files. Documents as Markdown, spreadsheets as CSV, the calendar as a real .ics, notes one file per note, the Record Suite's registers as CSV. Those are the real thing rather than an export, so they are useful on the second machine whether or not you open this site there at all.
It does not get you the app's own state. What each app keeps in the browser, which is the copy the app actually reads, stays in that browser. Open this site on the second machine and it starts empty, then writes its own work into the same folder beside the first machine's. The folder is the shared thing; the browsers are not.
Nothing merges. Editing the same document on both machines in the same afternoon will produce two versions and no warning, because there is no server watching to tell you. Two-way sync is genuinely hard, and pretending to do it badly is worse than not doing it. Treat it as one machine at a time.
When the two machines are not on the same sync, Settings has the other route. Download everything as an encrypted bundle writes a single .obscura file holding every app's state, locked with a passphrase you choose, using AES-256-GCM with the key stretched from that passphrase. Move the file however you like, including through somewhere you do not trust, and restore it on the other side.
That one does carry the app state, not only the files, so the second machine opens with your documents, your notes, your task board and your settings exactly as you left them. It is a snapshot rather than a sync: the moment you restore it, the two diverge again.
This is the request that comes up most, so here is the real reason rather than a roadmap.
This site sends its browser a Content Security Policy that ends with connect-src 'self'. That line means the page is permitted to open a network connection to exactly one place: back to obscuraos.com. Not to your Nextcloud, not to your WebDAV server, not to anywhere. It is enforced by the browser rather than by our good intentions, which is what makes the claim on the rest of this site checkable: open the network tab, use any tool, and see that nothing goes anywhere. A WebDAV button would require relaxing that line to let the page reach arbitrary servers, and the moment it is relaxed the guarantee is gone for every page on the site, not just the one with the button.
There is a second obstacle underneath the first. A browser will not let one site make requests to another unless that other site sends headers inviting it to, and a default Nextcloud, ownCloud or Apache WebDAV does not send them. So even with the policy opened up, it would fail for most people, and the ones it worked for would be the ones who had already reconfigured their server to accept requests from a website. That is a worse security posture than the one they started with.
The honest position is the one above: the folder is a folder, and your sync client is better at syncing than a browser tab could be. Nextcloud's own desktop client, Syncthing and the rest already handle conflicts, partial writes and machines that are asleep. Putting the folder inside one of them gets you a better version of the feature than a button here ever would.
Syncing is for your own machines. For somebody else's, KEYRING encrypts a file to their public key in the age format, which the age program on their machine will open. CAPSULE locks a file with a passphrase you tell them another way. LOCKBOX makes an encrypted note that opens in a browser without installing anything at all. None of the three involves an account, and none of them puts a copy on a server on the way.
Wherever you chose when you pressed the folder button on the home page. The browser remembers the handle rather than the path, so it may ask you to point at it again after a while, or if you moved it. Inside it you will find a Workspace, Sovereign Suite, Record Suite and Notes room, and a README explaining what is what.
No. The folder is written to, not read from, except when you restore. Edit a document there and the site will overwrite it the next time that document is saved. Two-way sync is the hard problem, and this does not claim to have solved it.
No, and deliberately so: the files are plain Markdown, CSV and .ics precisely so that they outlive this site and open in anything. If the disk needs to be encrypted, encrypt the disk, which every operating system can now do, or keep the folder inside an encrypted volume.
Phone browsers do not offer the folder API, so the folder is a desktop feature. On a phone everything still works and is kept in the browser; move work across with the encrypted bundle in Settings, or by downloading what you need.
Not a hosted one. An account and a server is the thing this site exists not to have, and adding it would make every other claim on the site weaker. If sync arrives it will be between your own machines, with the keys held only by you, and it will say plainly what it can see.