Need more info. Is this a bedroom? Just one window? How big? It’s nearly impossible to answer without a picture.

OK, it’s a bedroom, but please post some pictures.

Just one window. 3mx3m.

I would do a Venetian blind. Looks like you need privacy. Blinds are great for light control and privacy.

In my opinion, valances are dated.

The window is too small for a fussy curtain.

Add color and texture in bedding, rugs and wall art. This window can just be functional and recede into the background.

That valance shown above looks dated because of its shape. A simple straight across valance would be better…. For under the cornice: Do you need continual daytime privacy or just night time. If continual daytime, a Venetian blind may be the only option (or interior shutters.). If not, a simple pull down - accordion-pleat style that folds up under the cornice is better.