When grouping items/subitems by a column (grouping by something other than the original groups used in the main view) you can’t exclude certain options from the column you have chosen to group by.
e.g if I chose to name my groups by colour in the main view, but in the timeline view I wanted to group by a dropdown column called ‘deliverables’ in the timeline view and an item/subitem has multiple deliverables assigned to it (e.g email, newsletter, SMS) I will see that item repeated across all teams when I only want to see it ONCE. In the settings I can only exclude groups from the main view so could exclude red etc… but what if I want to exclude SMS so I only see emails and newsletters?
As the item/subitem contains multiple dropdowns alongside the option you are filtering for, it will include ALL the dropdowns even when you try to filter for only one or two dropdown options