IMO you should not have to enter the Tabid for a menu, but tha'ts a different subject :-)
I also find ist annoying that you cannot see the tabid any more, mainsly when resolving redirct issues etc.
Not a fix but a workaround:
I include our https://www.40fingers.net/Products/DNN-Stylehelper in my theme's, it can render the TabId as a class of the Body tag.
You can use
< fortyfingers:STYLEHELPER ID="sh3" AddBodyClass="True" runat="server" />
Which will add a lot of context classes to the page or:
< fortyfingers:STYLEHELPER ID="sh4" BodyClass="id-[Page:Id] " runat="server" />
Which will only add a class for the TabId (to the current Page)
< fortyfingers:STYLEHELPER ID="sh5" IfRole="Administrators" Content="This Page TabId = [Page:Id] " runat="server" />
Which will show the id in the page for administrators only.