Different infill levels in a print

I have an Ender 3 S1 plus and am using creality slicer 4.8.2:216 on my Mint cinnamon laptop. I would like some parts of the item I am designing to have a a high percentage infill but most with perhaps 10%. Is it possible to do this? I have seen various suggestions but none seem to do it. One was to use a support blocker. I can create one, resize it and move it but don’t know how it is of use. Say I want a simple cube with the lower half having a high infill and the top a low one. Do I create two pieces, sit one above the other with the blocker in between and then slice it or do something else?