City villa subtly modern 218 sqm

That's called a Lichtband

What still bothers me about the draft is the living-dining area. However, it is not optimal in the old house either (69 sqm in an L shape, but only 9 sqm kitchen). I would be very grateful for ideas on how this 66 sqm area could be better designed.

I feel the same way. You practically cook in the living room and live in the kitchen. That is certainly communicative, but it can hardly hide the associated kitchen chaos during family celebrations. Would it be an option to move the living room area into the bay window and have the dining area where the kitchen is now? Then the kitchen would be in the current living area, which could be spatially and visually separated by a piece of wall. This would, of course, also mean that the utility room/bathroom and the workroom would swap positions, which would have consequences for the upper floor, where I am bothered by the fact that three rooms have some corners around the hallway.

... based on the overestimation of the contribution that direct sunlight makes to this illumination.

not quite. Rather based on 12 years of living experience with a southwest-facing living room of the same size. The advantage becomes apparent during the darker seasons. In summer, it’s practically irrelevant, as sufficient light comes in everywhere.

To separate the living area a little and make better use of the space, I would make a room divider on which the TV is mounted.
Something like this:

I haven't read the thread, but I always wonder what you want to fit into 218 sqm, apparently without a [Einliegerwohnung]?!? We are moving soon into 120 sqm for three people and I think that's okay, could also be 140, but no more.

to separate the living area a bit and make better use of the space, I would make a room divider on which the TV is mounted. Something like this:

... I hadn’t even had such a room divider on my radar, great idea, thanks