Sync chain - device which is no longer mine (sold device)

FYI The following information is from a previous post that may help.

The trashcan is not displayed if the browser version is less than v1.18.19 which is very old. Prior to this version browser does not support self-delete, so there is no trashcan icon next to such devices.

In your case I doubt you had such old version, but I don’t understand why happens. You can check it at brave://sync-internals/ => Sync Node Browser tab => Device info => choose your device => check MTIME field, it corresponds to the last time when the device was active, and chrome_version field to check the version. This may help to understand why there is no trashcan button.
Source: I got a laptop stolen and now I cannot remove that device from the Sync chain