Hi @MiguelDeNeve,
To answer your question:
I think the gallery pressed button can only change color if pressed and doesn't stay that way. Am i correct?
Answer: Generally, the button could change color once you click it, it does not change until you click another button in the Gallery.
Do you want to click different buttons to make the corresponding data cards visible and highlight the button in your Gallery, right?
Well, if so, you need to highlight buttons as long as it is pressed, right?
Here is a simple demo based on above assuming.
I set the Text property of the Button with ThisItem.ID, so the Button will directly display ID like 1,2,3,4
1). Set the onSelect property of button as below:
Set(Pressed,true);If(Pressed,Collect(colId,ThisItem),Remove(colId,ThisItem))
2). Set the Fill property of the Button:
If(ThisItem.ID in colId.ID,Color.Red,RGBA(56, 96, 178, 1))

3). Optional: if you want to reset th variable or clear the collection, you could add a reset button and set OnSelect to:
Clear(colId);Set(Pressed,false)