Hi @SOL24 ,
According to your description, I've made a test for your reference:
1\ Add a combo box control 'ComboBox1' and set its Items property to:
["Planning - values","Planning - market","Planning - sales","Execution - Data","Execution - Risks","Marketing - social","Marketing - Enviroment"]
Set 'ComboBox1' 's Onchange property to:
ClearCollect(Test,{Value:""});Clear(Test);If(Or("Planning - values" in ComboBox1.SelectedItems.Value,"Planning - market" in ComboBox1.SelectedItems.Value,"Planning - sales" in ComboBox1.SelectedItems.Value),Collect(Test,{Value:"Planning"}));If(Or("Execution - Data" in ComboBox1.SelectedItems.Value,"Execution - Risks" in ComboBox1.SelectedItems.Value),Collect(Test,{Value:"Execution"}));If(Or("Marketing - social" in ComboBox1.SelectedItems.Value,"Marketing - Enviroment" in ComboBox1.SelectedItems.Value),Collect(Test,{Value:"Marketing"}));Reset(ComboBox2)
2\ Add a combo box control 'ComboBox2' and set its Items property to:
["Planning","Execution","Marketing"]
Set 'ComboBox2' 's DefaultSelectedItems property to:
Test
3\ The result is as follows:

Best Regards,
Wearsky
If my post helps, then please consider Accept it as the solution to help others. Thanks.