Hi , @lunalovegood
As the test data here in the Button-OnSeletc:
Set(Data,[[{Name:"zyy2",age:1},{Name:"zyy2",age:2}],[{Name:"zyy3",age:3},{Name:"zyy3",age:4}],[{Name:"zyy4",age:5},{Name:"zyy4",age:6}]]);
Set(TestData, Ungroup(Data,"Value"));
We can use this code in the Combo box -Items :
Distinct( TestData, Name)
Then we can select the Name in this Table:

And if we want to filter the Gallery we can create a button and use this code on the Button-OnSelect:
Set(FilteredData2, Filter(TestData,Name = ComboBox2.Selected.Value ))
And Then we put the FIlteredData2 in the Gallery-Items:

Then we can filter this Gallery:

If you wan to mutiple selected in Combo box , you can also try to use this code on the Button-OnSelect:
Set(FilteredData2, Filter(TestData,Name in ComboBox2.SelectedItems ))

If I misunderstand what you mean, you can describe your needs and your expected outcomes in detail so that we can better help you.
Best Regards,
Yueyun Zhang