Venetian blinds and roller shutter motors - can a wireless remote control be retrofitted?

I don't get it, when I connect gray and brown as in the circuit diagram (like in the photo), nothing happens when I press the switch down. Now if I put the gray on the brown cable and the switch is pressed down, the blind goes down, indeed down.

One thing upfront:
I am not an electrician and what I write here is not an instruction or anything similar! I can only strongly recommend you act very, very cautiously and, if in doubt, ALWAYS consult a REAL electrician!!!

When I look at the other picture you sent, I interpret:
N - blue
L - black (the single one) (here there should ALWAYS be 230V regardless of the switch position)
L_Hoch - phase for up
L_Runter - phase for down

You have to connect the Shelly 2.5 as follows:
N = N (blue)
L = permanent phase (in your case probably black where there is ALWAYS 230V)
SW1 = phase coming from the switch for up
O1 = phase going to the roller shutter for up
SW2 = phase coming from the switch for down
O1 = phase going to the roller shutter for down

In the first step, check whether 230V is present on the permanent phase. To do this, connect this and neutral to the Shelly and see if it turns on. (Always turn the fuse off/on)
You can check if it is on by seeing if you find a Shelly WLAN

Then connect the phases coming from the switch and going towards the roller shutter...
(again, always WITHOUT the fuse inserted and NO POWER on it)

If everything is connected correctly, download the Shelly app and integrate the Shelly into the WLAN.
Then set the button type to Momentary and configure and calibrate the Input Buttons Mode according to the switch (or push button)... done.
(Don't forget the firmware upgrade)

One thing in advance:
I am not an electrician and what I write here is not an instruction or anything like that! I can only recommend that you act very, very carefully and ALWAYS consult a REAL electrician in case of doubt!!!

When I look at the other picture you sent, I interpret:
N - blue
L - black (the single one) (230V should ALWAYS be present here regardless of the switch position)
L_Hoch - phase for up
L_Runter - phase for down

You have to connect the Shelly 2.5 as follows:
N = N (blue)
L = permanent phase (in your case probably black where 230V are ALWAYS present)
SW1 = phase coming from the switch for up
O1 = phase going to the shutter for up
SW2 = phase coming from the switch for down
O1 = phase going to the shutter for down

In the first step, check if 230V is present on the permanent phase. For this, connect this and neutral to the Shelly and see if it turns on. (Please always turn the fuse off/on)
You can check if it is on by seeing if you find a Shelly WLAN

Then connect the phases coming from the switch and going towards the shutter...
(again ALWAYS WITHOUT the fuse inserted and NO POWER on it)

If everything is connected correctly, download the Shelly app and connect the Shelly to the WLAN.
Then set the button type to Momentary and configure and calibrate the input buttons mode according to the switch (or button) ... Done.
(Don't forget the firmware upgrade)

Thanks. No problem, I'm not an electrician either.
Just kidding. All good.

It worked, I just had the phase in the wrong L the first time, so it didn't work.

Now it works with Alexa too. But when I look at the commands, it's rather not suitable for venetian blinds. I can hardly imagine hitting the right slat angle with Alexa. :-p

For venetian blinds rather only for up / down ... hitting the angle will be difficult.

I use the Shellys for the blinds ...

For venetian blinds rather only for up / down ... getting the angle right will be difficult.

I use the Shellys for the roller shutters ...

I agree. Thank you.

Damn! Seeing it like this, I should have wired the whole thing in the connection boxes before the painter plastered them... At least I would have had plenty of space then ;-(