no output device found in y Macbook Air

Open System Preferences >> Sound >> Tab called Output and see if Internal Speakers is chosen

Have you done a PRAM reset, CMD+Option+p+r...

http://support.apple.com/kb/HT1379

In fact, do 3 in a row, takes a bit of time.

Intel-based Macs: Resetting the System Management Controller (SMC)...

http://support.apple.com/kb/HT3964

Thanks very much

Update to mac OS Big Sur should work

no show internal speakers

no output device find

what shall i do ?

no output device find

what shall i do ?