My MacBook Air when turned on shows a white screen with a flashing folder with a question mark inside

Did you try this? ! If your Mac has newer M1 Apple Silicon

the instructions here may not directly help.

• If your Mac starts up to a question mark - Apple Support

https://support.apple.com/en-us/HT204323

There are a few other things to try, those here could help:

• Mac White Screen? How to Fix a White Screen on Boot | osxdaily

https://osxdaily.com/2016/12/10/mac-white-screen-boot-fix/

"Often simply resetting NVRAM / PRAM is sufficient to remedy a white screen Mac issue:

Reboot the Mac,the moment you hear boot chime, hold down the Command+Option+P+R keys

then, on 'second boot chime' then release 4 keys, the NVRAM has been reset." Timing is everything.

If not, there may be further troubleshooting to be done. Last not

least, try startup in macOS Recovery; maybe reinstall the macOS.