Acquisition of a vacant farmstead in the outer area

If it is not technically necessary, then it is not necessary. Tongue and groove will probably be more stable overall (warps less because the boards hold each other) less air comes through the cracks and you cannot look through the cracks (when the air is dry). But your solution seems stable enough to me anyway and the wind will whistle little behind the boards ;)

Theoretically it is nothing other than tongue and groove if each board is screwed from one side and wedged against the next from the other – and that’s how we built it. It should not whistle in a KfW55-EE house either. The walls behind were fully reinforced beforehand. The blower door test caused no problems at all for the residential barn (nor for the house in general).

because it is not so perfect that belongs to me to the subtleties of building: When is something perfect? Perfection in general also includes the amount of work, durability, environmental compatibility and many details that are not visible at first glance,

"is screwed from one side and wedged against the next from the other side"

I don't quite understand that, because the side that, when screwing, presses against an already existing board, you can't screw in invisibly, can you? But we don't need to go into technical details here...

I like your construction, I find - what I see - successful, wish you further good progress and look forward to seeing new things here :)