Pleated blind for fixed glazing / suggestions?

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Sorry - but that is wrong, and not because I claim it. It can be measured and has been scientifically measured many times. The heat is already BEHIND the glass, that is, INSIDE the living space.
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Agreed! Sun protection is most efficient when installed on the outside.
However, when comparing windows with/without a pleated blind, I would expect the pleated blind to block some heat, depending on where the sun rays hit without the pleated blind. Without the pleated blind, the sun rays would hit and warm the objects inside the room.

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:DD This is probably not exclusively a venetian blind problem. If a pleated blind, roller shutter is down or a door is closed, generally it is hard to go in and out :D or only once and then a craftsman has to come.
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Why can’t a door with a pleated blind be opened?

You can't really argue about taste, as everyone knows. ;)

I find pleated blinds visually quite appealing. We now have some in the bathroom. Self-installed, clipped on, and standard stuff from Amazon (I know, a crime^^). I'm actually quite satisfied with them. They look great. And we don't move them very often anyway. There are only a few days a year when we'd like to pee away from the neighbors' eyes, so they usually stay down. :D

I'm currently pondering the rest of the house. If I really want to darken it there, I'll use the roller shutters. But as the windows are, it just looks uncomfortable and very sterile / like a construction site. I'm thinking about installing curtain rods and decorative curtains. I wonder if that's still allowed or if you'd already be stoned for something that old-fashioned. ;)

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I find pleated blinds quite visually appealing. We now have some in the bathroom. Self-installed, clamp-on and standard goods
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So? Are the windows now leaking (more)? :)

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I'm just thinking about installing curtain rods and decorative curtains. Wondering if that's still allowed, or if you'd get stoned for such an old-fashioned thing. ;)

In my former rental apartment, there were sliding panels on three rails from a Swedish "designer" in front of the windows. I didn't find that bad. We're considering mounting something like that in the stairwell as decoration.

Well, I can think of various points. ... All in all, I find pleated blinds a good compromise of all things.

You forgot the biggest problem: susceptibility to wind. On the financial side, besides the additional cost for the venetian blinds, a wind sensor and a Somfy or similar have to be factored in. And when there is strong wind, the parts go up. Even at Lake Constance (which is rather known for calm winds), this often enough becomes a problem. As nice as it is to shade with venetian blinds without sitting in complete darkness, it simply doesn't suit about 10 days a year here. Accordingly, we are installing roller shutters and additionally pleated blinds in the office, preferably adhesive ones.

Why can't a door with a pleated blind be opened?

:D That's true again, although we have two internal blinds/pleated blinds attached to the lintel and not to the window frame, which can sometimes cause problems. But if attached to the frame, then of course it was nonsense from me. o_O

There is known to be no arguing about taste.

Yes, absolutely even. One just rarely comes to an agreement. But it can still be fruitful... or terrible.

I'm just thinking about putting up curtain rods and decorative curtains. I wonder if that's still allowed or if one would already be stoned for something so old-fashioned.

Curtains can look really great, as always, it should all fit together. I could also imagine having a really nice carpet floor upstairs again, although that's no longer mainstream nowadays. There isn't just ONE thing here either.

As nice as it is that you can shade with Venetian blinds without sitting in total darkness, on about 10 days a year it just doesn't fit here. Accordingly, we install roller shutters and additionally pleated blinds in the office, preferably glued on.

That certainly applies on some days and another system simply has its pitfalls or disadvantages on other days or in other situations. I generally prefer the jack of all trades; if anyone finds one, please contact me immediately.

Plissees or double roller blinds? In my former rental apartment, there were sliding elements on three rails from a Swedish "designer" in front of the windows. I didn't think that was bad. We are considering installing something like that in the stairwell as decoration.

I had the sliding parts from Sweden in the rental house for the last 10 years, I can't stand them anymore. :D I would prefer something more in the country house style. I find the nicest things on Pinterest (once again), but I don't know where to buy something like that in this country.