A circle with a line through it on your Mac startup screen shows that your new MacBook can't boot from the macOS version on the startup disk. Thus, your new MacBook refuses to boot up.
To fix your new Mac that boots to a circle with a line through it, you can try these workarounds:
1. Run Disk Utility First Aid to check and repair the startup disk
- Press the power button for a few secs to completely shut down your MBP.
- Press the power button and meanwhile press the Command + R keys until seeing the Apple logo appears to enter into macOS Recovery mode.
- Choose Disk Utility.
- Select your Mac startup disk from the left sidebar and click First Aid.
- Restart your Mac.
2. Reinstall macOS in Recovery mode
If your new MBP still won't boot up, re-enter Recovery mode and click Reinstall macOS. If your Mac still won't turn on, send your detailed information to the Apple support team to get help.