Tabs are not directly synced, you will have to open them all again and update them manually. However, that does not mean they are not being synced at all. You can access them though opera://activity/ when logged into Opera. A button for this is available to add to the sidebar in [Sidebar Setup] (three dots at bottom of sidebar) > [Opera Tools] > [Tabs], or you can hover next to the "Tabs" text and press the little "open in new tab" icon that pops up.