@Mathieu-And-Kunj0thank you for the nice words!
I like your listing a lot. What a beautiful building! You also have lots of vintage/antique furniture that that works well and that I'd love to get my hands on 🙂 I will have a more detailed look and make some suggestions, but off the top of my head...
I think the living room could do with more colour or pattern on the walls. It's a big room with high ceilings, so I think it could take something quite dramatic, but you don't have to go too dark or too bold if that's not your thing.
A trick I learnt, and have started applying in my own house now, is that painting the woodwork (doors, window frames, skirting, picture rails) in the same colour as the walls can look very chic and this works best in rooms with high ceilings. You need to use a paint for interior wood (I go for eggshell as I think the matt finish is much nicer than gloss) but in the exact same colour as the walls. I do like the gold highlighting on the panels though.
Can I ask if the floor is new or restored? Is it laminate or wood? Sorry, I can't tell from the photos. If it's wood, I would think about staining it or possibly doing some kind of washed paint effect, as it looks a bit too new and shiny for the rest of the decor, but I understand that is quite a big job!
One of your bedrooms has beautiful antique beds, but the other has very modern furniture. I would think about replacing that as and when you can with something more in keeping with the property. Overall, it would be good to try to incorporate more of a flow in the style and mood of the rooms throughout the apartment. I know this is a bit tricky though with kitchens and bathrooms if they are already modern looking.
I love thinking about this sort of stuff, so I will definitely have another look when I have more time and maybe include some photos for inspiration.