It sounds like the correct firmware needs to be uploaded and the drone needs to be calibrated.
I looked at the Drone Building Tutorial video, and it seems to have left out the entire step for flashing the flight controller firmware and installing Mission Planner. Are you enrolled in “How to Build a Raspberry Pi Drone”? You should follow that video and in the Pre-Flight steps it discusses flashing the firmware.
The course includes steps for binding the X6B receiver. Also refer to the FS i6x manual (section 4.2). Finally, here also is one Youtube video that addresses it.
Using MP load the firmware and follow the calibration steps, including radio and esc calibration. Use the frame type as indicated.
Leave the safety switch. As its name implies, it’s for safety!
Include the smoke stopper in your power feed whenever powering up for the first time, or whenever you change anything to protect the electronics. Then if the system checks out remove it before you proceed further.
In addition to viewing the Drone Dojo videos you should read through the Ardupilot references.
It is also important to ensure the copter is properly tuned. The courses touch on a basic tune which should be fine for this kit, but you might want to check out this and this. The last reference is good but 3 years old, so you might want to check further.
Also learn about failsafe modes to ensure safe flight.
Let me know how it goes,.
Jack