How to make windows opaque?

I think we will go for the pleated blind

There are different types

one to clamp between the window and the frame
over time, won’t the clamps press the window seal and isn’t the window still properly sealed then?

Then there is installation in the window groove by drilling or gluing (which can be replaced if necessary)

There are different kinds

We chose a double roller blind in the dressing room, it protects against the sun, covers the entire window, and in winter we leave it "normal" so that light can come in, but nobody can see anything, and it is super easy to install.

That is in the bathroom on the east side. Opaque film at the bottom. Ordered from Amazon. There were 2 pieces included, or a kind of roll to cut. First piece messed up, second installed. Has held for 3.5 years. Above you can see [Plissees] that can be opened from the bottom and top with clamp mounts.

Try it first with the foil. It is available for €10 at the hardware store and can be installed and removed idiot-proof. Plissee costs ten times as much.

I can also recommend the film. We have such a film in the bathroom, where we left the upper approx. 50 cm of the window open. Even so, you can't see anything in our case and we have more light. The installation is simple. You don't need any tools. The only disadvantage so far was that the children a few times wanted to work on the lower corners of the film because they wanted to look out of the window.

The films are very easy to apply and come in so many different and really pretty designs. We have one in the guest bathroom, then another on the glass door in the bathroom because my boys felt watched. Of course, you can see the outlines, and whether you feel unobserved there is probably only found out once you have applied them. That would be the first alternative for me now. We also have pleated blinds on other windows, but we had to drill into the wooden windows because the mounting with the hooked fasteners was useless and the windows simply could no longer close perfectly. The advantage of the pleated blinds is that you can move them from bottom to top and determine the area where light can enter yourself. Or a very simple method, which I have in the parents' bathroom. Cafe curtains that can be inserted into the frame with a rod. A bit old-fashioned, but there are also modern versions of that.