I would like to comment on the @cseder answer, but I don't have enough reputations point. So I write a new answer.
I followed all the steps mentioned but the Simulator and Xcode did not show the simulator devices. To see and launch all the simulator devices I had to launch the programs as "sudo" but this is a bad practice. As I read, launching Xcode with "sudo" also the iOS app will be launched with the root privilege.
So I found this answer: I want to change path of ~/Library/Developer/Xcode/iOS DeviceSupport to my External Drive
Here not the whole ~/Library/Developer folder is copied but only the ~/Library/Developer/Xcode folder. Now I see all the devices. Probably they are still on the internal storage but I saved enough space moving Xcode and the Xcode folder.
Do you have other suggestions to move all the Developer folder and don't have this issue?