Click on the List All Tabs icon, there will be a section called Recent tab groups. The List All Tabs icon will look like either one of the two images attached below, depending on whether it is on the toolbar or on the tab bar.

If you cannot find the icon, it can be readded to the toolbar via application menu (three horizontal lines) -> More tools -> Customize toolbar -> drag the List All Tabs icon.

List All Tabs doesn't appear either in the task bar or in More tools - Customize toolbar.

If you are fine with having to reconfigure your toolbar setup, you could try to Restore Defaults in More tools -> Customize toolbar. The default toolbar should have the downward facing arrow in the top right, which is the List All Tabs icon. And next time, please create a new post instead of replying on a many month old question, thanks.