Dynamics are not reflected at all.

I don't see any dynamic markings here? In order for us to investigate, we'd need precise steps to reproduce the problem you are hearing.

If you mean, "velocity" settings don't affect the volume of notes, that's true - velocity isn't used to control volume on instruments that support single note dynamics (that is, the ability to crescendo on one note). Instead, continuous controller messages are used. if you need to be able to control velocity note by note, you'd need to disable single note dynamics in staff/part properties, and switch to non-expr sounds. In general, though, you should be using actual dynamics markings, not velocity, to control volume.

Sounds, not instruments. Use the sounds without "Expr."

Velocity settings are not compatible with "single note dynamics" (e.g., crescendo within a single note) in MuseScore 3. So if you wish to use velocity settings to override the actual dynamics markings in your piece, you need to make sure the staff is set to not use single note dynamics, via Staff/Part Properties. And then you need to choose a sound for the staff that doesn't rely on single note dynamics, by making sure the sound is not an "expr" sound. Sounds are selected in View / Mixer as noted.

Generally, though you starting point should be adding actual dynamic markings. Velocity settings are used only to allow certain notes to deviate from the dynamic marking.