Welcome to the forum. 
They all exist, but are not all available on all difficulties. If you have the base game then there are more on Normal than on Elite and more on Elite than Ultimate. If you have the Ashes expansion only then Normal still has more than Elite and Ultimate do. If you have the Forgotten Gods expansion as well then that is reversed with Ultimate having the most, then Elite and the least on Normal. That said, with Forgotten Gods there are a total of 157 shrines over all difficulties.
Rather than use the World Map, you’d do better to use the Checklist and then select the difficulty you’re on to see what shrines are on that difficulty.
https://www.grimtools.com/checklist/shrines/normal
There are also these 2 lists for base/AoM and FG shrines depending on what you have of the game which tell you which ones are available in each difficulty and what their requirements are.