I’ve had very good results using the most reflective mirror privacy films. All depends on the lighting though and your preparation. One or two specks of dust can ruin a whole window.
Did these for a customer. View from the LIGHT side (mirror) and from DARK side (see through)…will flip during the day when it’s brighter outside as per the intended use. Some people still take the (every police movie) one-way glass too literally and demand that you put it on the other side like it’s some magical film.
It will never be as good as a real mirror, but comes pretty close for a tint film. Putting a solid black or white on the back of it might enhance it as just a mirror but I’ve never tried it.
Got mine from the window film company.