Dashboard - how to remove the OVERVIEW tab? What is this tab? why can I not set filters?
The overview tab will show all the widgets that you have made 'Favourite' across all other tabs. (individually for you within the Settings configuration on each module tab). Especially this is a 'favourites tab' of all of the widgets that you want to see across all the tabs. The reason you cannot filter is due to the fact that it is bringing it from the individual tabs which has the filters already applied.
For example, you have "Top Risks" which is coming from your Risk tab > Settings > Favourites ticked.
To remove the overview tab (which is essentially the view of all your favourite widgets showing from their specific tabs across all modules) you just need to go and un-select the favourite button on them:
Do this for all of the widgets ‘Settings >Config page’ showing and it will disappear: