I used the dropdown menu at the top of the Sidebar (displaying vertical tabs) where you can manage your tab groups.
I clicked the "+" button in the lower left corner to add a new tab group ("Cooking").
After the Cooking tab group was created from this menu, it appears in the dropdown list, but NOT in the icon row of tab groups at top of the Sidebar. See below:
In another profile, the same issue occurs. See below:
Safari doesn't have vertical tabs with tab group icons at the top so I cannot test this there.
I expected any tab groups created within the dropdown menu would appear in the same icon row at the top of the Sidebar as tab groups created from clicking the "(+)" button in that row.
Version 1.0.6 (145), WebKit 624.1.7
Sequoia (15)
