@mychakk In version # 70.0.3728.71 (for Linux) the flag "search-in-open-tabs" unfortunately is no longer available.
As you mentioned, the magnifying glass icon has a set of closed and open tabs, but only for the current device
Also, the Tabs icon for the side bar is still buggy. It is sometimes available and sometimes is missing. However, if the icon is missing you can still access to the list of tabs by typing opera://activity in the address bar.
So far, it seems to be the only option since the "search-in-open-tabs" flag has been removed.