Hi @BenGillard,
Do you want to filter your Gallery items based on the Checkbox control?
I have made a test on my side, please take a try with the following workaround:

Set the Items property of the Gallery control to following:
Filter(
Search('20181122_case14', TextSearchBox1.Text, "ProductName"),
If(Checkbox1.Value=true, Status.Value="Approved",true)
)
On your side, you should type:
Filter(
Search(DS_Howdoi, TextInput1.Text, "Title"),
If(Checkbox1.Value=true, FilterColumn="Key Word",true)
)
Note: The FilterColumn represents the column in your SP list, which you use to filter your Gallery items based on the Checkbox control.
The GIF screenshot as below:
More details about Filter function, please check the following article:
Filter function
Best regards,
Kris