To make the caramel, in a saucepan over medium-high heat, add sugar and water. Cook without stirring until the sugar has melted and becomes light amber. Cook until the sugar turns a deep amber color. Remove it from heat and pour the caramel into the ramekin, swirling to coat the bottom.
In a large saucepan, combine 1/4 cup of sugar, orange juice, zest, cinnamon sticks, milk, and heavy cream. Cook the mixture on medium heat until the edges start to bubble. Remove the pan from heat and let it steep for 15 minutes.
In a large mixing bowl, whisk the eggs, egg yolks, and remaining sugar.
Pour the warm milk while whisking the egg mixture until smooth.
Strain the custard through a fine-mesh sieve in a spouted clean bowl.
Gently pour the custard over the caramel layer, taking care not to disturb the caramel.
Pour 1 1/2 cups of water into the Instant Pot. Cover the ramekin with foil and set it on the Instant Pot steamer rack or trivet. Carefully lower the steamer rack into the Instant Pot.
Lock the lid and Pressure Cook on high pressure for 14 minutes. Let the pressure release naturally for 30 minutes.
Open the lid and carefully remove the ramekin from the pot. Remove the foil and let the flan cool to room temperature.
Transfer the ramekin to the refrigerate and let it chill for 4 hours or overnight to set.
To prepare the segmented blood oranges, cut the tops and bottoms off the blood oranges then cut the white pith away from the outside of the fruit.
Cut the wedges of fruit away from the membrane, letting the fruit and juices fall into a prep bowl.
When ready to serve, run a sharp knife around the edge of the ramekin to loosen the flan. Place a serving plate over the ramekin and invert the flan onto the plate.
Top the flan with the segmented blood oranges and serve immediately.