Outdoor lamp motion sensor

Yes, you can do it that way. They then function like a two-way switch so that the light can be turned on either by the sensor or by the switch. However, pay attention to the connections when buying the motion detector or get advice. Also, you should replace the lamp, otherwise it won’t work for the reasons already mentioned.

At the moment I have neither a lamp nor a motion detector, so that's fine. I think with a normal lamp and a motion detector it should work.

Definitely. You don't need to consider anything for the lamp except that it is suitable for outdoor use. Then everything will be fine.

In addition, the cable leading outside should have 5 cores. One as permanent voltage, one switched by the switch, one as neutral conductor (N = blue), one for grounding, and one remains unused

Furthermore, the cable going outside should have 5 wires. One as continuous power, one switched from the switch, one as neutral conductor (N = blue), one for grounding, and one remains unused

Well, at least it has that

Hm, another option: I'll take a lamp with an integrated motion sensor, but I'll only connect 3 of the 5 cables. That should work too, right? Then I'll switch the indoor switch to continuous operation, so the lamp has power all the time - but it only turns on when the motion sensor reacts. The other two cables would then be spare. That should work too, right?