Here is my version of the famous “Floating Cup” model. You can see that mine has a hidden Mickey in the coffee splash!
This model is designed to use washers to weigh down the splash. They should be 2" OD and ½" ID like these: https://a.co/d/cGHOK2I
There is a file of trapezoidal pins scaled to a range of sizes, used to attach the "splash" to the "stream" and keep them aligned. Choose the largest one that fits into the sockets in the "stream" and "splash" parts. Trimming their edges with a knife or clipper, or sanding them down may be required.
Thank you to @bwaslo_1772 for remixing the original model by HappyMoon.