I moved to pc from Xbox I want to play apex on my pc, but my rank is gone

Hey FaceTimeMeBro,

Just to add on to what Reece_FPS mentioned, as the leaderboards are separate for each platform you wouldn't see your Xbox rank carry over to PC. 

Your rank will be separate for each platform, however keep in mind that your end of season rewards are based on the highest rank achieved across all platforms, not just the one you're currently playing.

So, even if you're now playing on PC and are in Rookie, if you reached Gold 3 on Xbox (and don't reach higher than this on PC by the end of the season), you'll get Gold rewards at the end of the season and will be able to display those on any platform.