I expect (and hope) that you have choosen to include the LCL in the cross-compiling (in Setup+).
Normally, the cross-compiler only makes a FPC cross-compiler.
LCL is done when needed, by Lazarus, on the fly.
Correct ?
If so, uncheck. And build your x64 app with cocoa !
I will also make a not that I have to change fpcupdeluxe in this case.
(I never include the LCL myself)