Alfons Maria Mucha, known internationally as Alphonse Mucha, was a Czech painter, illustrator and graphic artist, living in Paris during the Art Nouveau period, best known for his distinctly stylized and decorative theatrical posters, particularly those of Sarah Bernhardt. He produced illustrations, advertisements, decorative panels, and designs, which became among the best-known images of the period.
More beauty: https://artvee.com/artist/alphonse-mucha/
Art Nouveau is so beautiful and yet so overlooked and forgotten compared to other styles.
I don't know much about it but I agree, saw a post with some Art Nouveau architecture that I loved, too!
If you get a chance, go to Riga in Latvia. They have whole streets of architecture in that style - https://theculturemap.com/art-nouveau-architecture-in-riga-where-to-find-it/
I'll try to post more. Thanks for the feedback.