What are UCI categories for cyclocross events? Having more than 10 years of MTB experience, I want to try my first CX race. However when I google for CX events in my country, the results contain some scary codenames called UCI C1 and UCI C2. In MTB enduro races you know that you have pros and amateurs riding the same course, just separated by the start times, so there is no worry to lag behind. In cyclocross it's a different story, I'm afraid to make a joke out of myself or even worse, ruin someone's run if I'm choosing a wrong event. So basically, how do I know if I can try one of those events? Do those events require some kind of bureaucracy (UCI license) to enter?
These are quite high-profile events. I think you do need a license, C1 and C2 are pro categories.

From a random website:


  What does UCI, C1 and C2 mean?
  
  That means some of the world’s best cyclocross racers will be right
  here in Rochester racing at the Rochester Cyclocross in Genesee Valley
  Park!  Including a bunch of current and past national champions, the
  competition will be fierce – so don’t miss a second of it! UCI stands
  for the “Union Cycliste Internationale”, they are based in Switzerland
  and they are the worlds governing body for professional cycling. C1
  and C2 refers to the level of international event – C1 is the highest
  level ( there are only SEVEN of these in the USA).


https://rochestercyclocross.com/frequently-asked-questions/

There should be non-UCI races around. In UCI races you have to have a frame with the right UCI-approved sticker and 33 mm tyres.  In amateur friendly races the riders are often not eliminated when lapped and can use wider tyres or even other types of bikes.

Note that in America there are often amateur categories as "side races" taking place on the same course during tha same weekend as the C1 and 2 races.