A work-around: save all open tabs into a bookmark folder; they should miraculously appear in your bookmarks across all the other devices.
To save all tabs: If you're on |Safari on iPhone or iPad|, long-click on the bookmarks icon and you will be met with: "Add Bookmarks for X Tabs." If you're on |Safari on Mac|, go to the Bookmarks menu and choose "Add Bookmarks for These X Tabs..."
If your bookmarks sync nicely, the folder just created will appear across all devices. Good job!
If bookmark sync'ing is not happening for you, go for the longer work-around detailed below.
Longer work-around: copy contents of the newly-created, saved-tabs bookmark folder onto the clipboard. Now paste the urls into a note in the notes app (that should sync easily).
To copy the tabs from |Safari on iPhone or iPad| to |Safari on Mac|: navigate to the bookmarks folder that you just created and long-click on it. Now choose "Copy Contents." Lo and behold, the urls of the tabs are now in the clipboard.
Note: I don't know how to copy a bookmark folder to clipboard on |Safari on Mac|.