If you just installed it from appstore then you need to open it and accept xcode license. After that some components will be installed. Then try to run local build server.
If it still cant find the xcode version then try to reboot your mac. I faced this too but the problem was Adobe AfterEffect. If any heavy software is running in background then close that and try again.
Did you open Xcode and login with your credentials at any point? I seem to recall having that as a must do step when I installed a newer version of Xcode.
xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance
To fix the error :
Vals-Mac-mini:~ valraemaekers$ sudo xcode-select -s /Applications/Xcode.app/Contents/Developer
Thanks for your help Erel , Buildserver is now running