Renovation of existing ground floor apartment - additional office

I would leave out the divider. It’s unnecessary. Is the door a round arch without a door leaf?
I would extend the “island” all the way to the support and keep it generous. Also raise it to counter height so that about 1.20 m remains in the middle.
The space near the fireplace will probably only be enough for a small table for four? Possibly buy a round extendable one. Or place it against the interior wall of the living room.

All round arches will be removed; there will be normal standard doors. What do you mean by “raise to counter height with 1.20 m in the middle”?
By the fireplace itself, I wouldn’t put anything at first, maybe except a narrow sideboard.

Tall cabinet = to the right of your dividing wall = probably refrigerator

Try moving things around in the living room yourself … I think there is no great sofa/TV position to be found.
And dining table, as Yvonne wrote, definitely does not fit below the kitchen peninsula, because that is the passage area to the private rooms.

That’s why this suggestion:

The suggestion is really good too, but I have two problems with it: 1. There is no window/natural light in the hallway. In the room you imagined as an office, despite the terrace door, I have little brightness because the roof overhangs very far in that area. So the whole room will be very dark. That’s why the idea of “making everything more open and removing the wall”…

tall cabinet = to the right of your dividing wall = probably refrigerator <-- What do you mean by that?

Kitchen: There is a wall next to the office door and to the right of it the refrigerator as the only reasonable tall cabinet possible in the kitchen. And it will definitely be a dark hole back there in the room.

https://www.hausbau-forum.de/attachments/Küche-hochschrank-Anbau-trenner-Eingangsbereich-331566-1-jpg.35773/

When I see this plan:
Isn't it even better overall in terms of spatial structures to leave the kitchen where it still is now (i.e., originally), but open the wall, then also the walls as drawn here, and place the office on the left side of the plan in the middle, that is, separated as a horizontal rectangle of 8 sqm in the upper area of the living room? The missing window in the exterior wall can be compensated by installing a strip window under the ceiling in the longer wall.
Then you have a chill corner, a large dining area in the middle, and a separate kitchen.
Light also comes from the kitchen into the room.
?

https://www.hausbau-forum.de/attachments/Küche-hochschrank-Anbau-trenner-Eingangsbereich-331566-1-jpg.35773/

When I see this plan:
Isn't it even better, overall from the spatial structures, to leave the kitchen where it still is now (i.e. originally), but open the wall, then also the walls as shown here, and place the office on the left side centrally, that is, in the upper area of the living room 8 sqm as a horizontally oriented rectangle separated? The missing window in the outer wall can be compensated for by installing a strip window under the ceiling on the longer wall.
Then you have a chill corner, a large dining area in the middle, and a separate kitchen.
Light also comes from the kitchen into the room.
?

Can you please draw it? I just can’t imagine it right now?
Many thanks

Something like that... I misjudged the pillar. There should be 3 meters between them. In everyday use, you could turn the table and place it against the wall.

Cool idea. I would just have to place it differently, since the entire south side is a glass front or doors to the terrace. And you meant to insert a light strip in the wall between the office and the living room?