What does "Device limit reached" mean?

Free accounts sync on up to 2 devices, and this dialog appears when a third tries to register. Remove a device you no longer use directly in the dialog, or on an existing device under Settings > Account (how removal works). The slot frees immediately, and the removed device stays visible under "Recently removed" for 72 hours. Pro lifts the cap entirely.

One quirk worth knowing: so that several browsers on one computer do not eat several slots, devices are grouped using privacy-preserving hashes of coarse machine signals, computed on your device with a per-account secret. A major browser update, or hardened browsers like Brave or Tor that randomize those signals, can land the same machine in a new slot for a while. You are never locked out - remove the stale entry and carry on.