The Vltava river is the best place for sunset, hands down. As the sun sets behind the Petrin Hill and the Castle, the golden light hits the Old Town towers and it’s just stunning. If you time a dinner cruise right, you start during the golden hour and transition into the night lights. It’s the best way to see the "Two Faces" of Prague in one sitting. Look at the link
https://alle.travel/en/prague/category/dinner-cruise for cruises starting around 6:00 or 7:00 PM depending on the season. You get that perfect glow on the water, and once the sun is down, the dinner service usually kicks into full gear. It’s a photographer's dream and a very chill way to spend the evening.