iCloud tab syncing was working fine until I upgraded to iOS 17.4 on my iPad and iPhone and now the way it works has changed.
If i close Safari with tabs open it works the same way it used to. My other devices, including my Mac on 14.3.1 will show those tabs as iCloud tabs on my other device.
Now though, if I close all tabs and close Safari, instead of the other devices showing no open tabs on my device, it just shows the tabs that had been open.
Syncing isn’t broken per se as opening new tabs and closing Safari will remove the old tabs, but basically tabs won’t sync if there are no open tabs. Effectively that makes clearing out the closed tabs from other devices impossible. icloud tabs has effectively become currently open or recently open tabs.
Basically tabs only sync when at least one is open.