I printed this with a 0.2 mm nozzle, I didn't test it with 0.4 but it should be fine. Print with Layer Height: 0.08 and upside down without supports (the model is already face down, so it should still be okay). I didn't need to postprocess it in any way, it was already good and it fits nicely onto the switch.
The first prototype had a curved surface, but it doesn't print well, so I opted for a flat surface and print it upside down so the keycap surface would be clean and have a nice texture on it (I use the P1S built-in plate)

HOW TO EDIT IT IN FUSION 360
Import the stl file, then go Mesh, Modify, Convert Mesh and press Okay (be sure it's set to Parametric, freemium options are fine). After that, go again to Mesh, Scale Mesh and set 0.1 as scale factor.
Now you can put custom text on the surface or even images (I recommend a 0.2 nozzle for these though).
You can put text via Fusion itself. About images, use Photoshop, Photopea, GIMP or other graphic tools to make a png file with only a color (black is preferable) and transparency. If your design has more colors, you can add some other color, like white or grey. They just need to be different, then you will apply your colors later on Fusion. Then google ‘’png to svg'' and open the Adobe page, and do the conversion there. After that, go back to Fusion, click on Insert on the top right, Insert SVG and then proceed from there by selecting the keycap face. To make the Yin Yang keycap, I extruded 0.01 mm on top of the face making a New Component, then applied the colors (by pressing A and clicking on Face) and proceeded to print it.
I'm open to questions and feeback as well as seeing your print pictures!