My MacBook Air screen shows a stop sign

On your MacBook is a version of macOS installed that is not compatible with the hardware, see

A prohibitory symbol, which looks like a circle with a line or slash through it, means that your startup disk contains a Mac operating system, but it's not a version or build of macOS that your Mac can use. 

1. Press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off.
2. Use Disk Utility to repair your startup disk. 
3. If Disk Utility found no errors or repaired all errors, reinstall macOS.
4. If you still need help, please contact Apple Support.

If your Mac starts up to a circle with a line through it - Apple Support

I had the same issue when I moved a drive from a MBP2015 with Monterey to a MPB2014 that only supports Big Sur.