How to make windows opaque?

Yes, you can completely look through the windows there

The dressing room has 2 windows, one to the side where the next semi-detached house is directly opposite and one to the garden where the neighbors opposite can theoretically look in but from a distance

The question is also, can you manage the frosted glass film yourself well?

Does the film get damaged or peel off with strong sunlight exposure (the window to the garden faces south)

Frosted glass film - how hard is it to apply, can you manage it yourself somehow?

If you're not too clumsy, yes.
Cut the film to size. Clean the window. Spray with soapy water. Peel off the protective film and also spray the film with soapy water. Stick it to the window and squeegee out the water. Let it dry. Done.

Ok, is the foil also heat-resistant in summer with strong sunlight?

What kind of mounting should be chosen for the [Plissee]?

As already mentioned, installation is easily done. We had it done ourselves, but simply because the price was very fair. It was hardly "worth it" to do it ourselves. The film is heat resistant; our windows, especially in summer, get full sunlight and so far (6 years) there have been no problems.

You can also install the film on just a part of the window, so I’d say on the lower 1.20-1.50m or so, depending on how the windows are visible. The advantage of the film compared to direct sample application is that you can also remove it again. Plissees would be the alternative, but you then have to close them beforehand. However, it simply depends on the exact situation, especially how exactly visibility into the windows is possible. If it is necessary to cover them completely, then plissees offer the advantage that you can make them partially transparent etc., depending on the situation. The frosted film is just “fixed.”

What kind of mounting should be chosen for the pleated blind?

A fastening that is possible without damage, and can be opened/closed from top and bottom

Totally forgot, we have pleated blinds that are mounted "on" top of the frame (with plastic holders) and then adjusted with a cord. They can be removed without any residue and are very flexible, so they are definitely a good alternative to frosted glass. The advantage is the higher flexibility because you can make the windows completely opaque, partially opaque, or raise the pleated blind completely.