It's necessary to use transparent filament
This is a print profile for a solid block of the material, achieving higher mechanical strength and transparency for transparent materials, The critical factor is 107% flow of the material, Slower speed, and a bit higher print temperature. You can use it on your own model, For example, optical lenses, Solid blocks with hollow inside, etc.
You can slightly tune it by yourself, for example slower print speed 10-15mm/s, or use higher extruder temp. 260°C.
For post-process, you can sand it with sandpaper, and for a totally clear look use a hot airgun, lighter, or torch.