How to delete devices that we no longer use from the synchronization chain?
It is not yet officially possible and an effort is underway to include this feature in the next update.
More information here: https://github.com/brave/brave-browser/issues/11232
I tell them to install the beta version and almost all the devices that I do not use were deleted from the synchronization chain. Including old facilities. Only the old devices that were used from the month of December 2020 are preserved.
I recommend that you install the beta version of brave to see if it can erase devices that you no longer use or installations that stopped syncing.