Do races exist, I’m thinking mostly MTB, but feel free to include road, for pros where they can NOT preview the course? I was having this conversation recently about being an age group MTB racer who shows up to most races having never ridden the course due to limited time off/budget. This year I had the cool experience of riding the UCI World Cup course before it was taken apart and there were so many sections where the right line made a world of difference. This led to a conversation about how it would be cool to see a race where pros have to show up and just ride - and it left me wondering if this exists in the real world 
Lots of “blind” enduro and stage races out there. Though I dont know of any on the WC level.
The BC Bike Race is a mutli day blind stage race. I think most of the people are on capable XC or short travel trail bikes.
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For road, most one-day races are heavily reconned by at least the top riders. And the rest will know the location of key pinch points and climbs. But for grand tours and such it’s impossible for riders to recon all of the stages. So even if the riders know “there’s a climb at kilometer 80” or “There’s a roundabout with 30k to go” they won’t have ridden it and things always look different at speed and in person. So in a lot of grand tours they are riding the less important descents blind (with maybe a garmin map up or a director telling them tight corners in their race radios).
For off road, it’s probably not super common at the WC level since the courses are so short and controlled that they have many walkthroughs and test rides. But on the domestic scene with more ‘adventure-y’ type races like Little Sugar or Peak 2 Peak in the US there are probably many pros riding those races without having pre-ridden most of the course.