Why do I have to install Brave on all devices first? It it not possible to add new devices for syncing afterwards?
You can just put your data on sync chain (cloud/server) and it will stay there. It does not need another brave browser, for the sync feature to work.
Click on the orange thing, then click on computer. Your data then will be store on the chain.
I have a lot of browsers (PC, Mac, Mobile Phone etc.) the message (sorry in German here) implicates that the order, where I install brave and start the sync is somehow important.