Here is an example.
In this example my SPList is Named StorageUnits
I have 2 checkboxes, checkbox1 and checkbox2.
Checkbox1 has text property of one of the possible strings found in the ContactName column of my splist
Checkbox2 has text property of one of the possible strings found in the ContactDepartment column of my splist.
The gallery below them has a Items property of
If(
And(Checkbox1.Value=true,Checkbox2.Value=true),
Filter(StorageUnits, ContactName=Checkbox1.Text || ContactDepartment=Checkbox2.Text),
And(Checkbox1.Value=true,Checkbox2.Value=false),
Filter(StorageUnits, ContactName=Checkbox1.Text),
And(Checkbox1.Value=false,Checkbox2.Value=true),
Filter(StorageUnits, ContactDepartment=Checkbox2.Text),
StorageUnits
)
This gives me all gallery items when nothing checked, only items matching either checkbox if only one is selected, and all items that match one of the two when both are selected (can change that to only items that have BOTH selected by changing the || to &&)