[PLUG] Linux audio on Macbook 12 inch

[VY]

Hello all:

I inherited an Intel based Macbook 12-inch from a friend who is retiring it.

The CPU is an Intel M3 chip.
I installed Linux Mint and everything is working fine except audio.
During audio playback, I can only hear sound on the 3.5 mm jack.
The on-machine speaker is dead silent.   The sound output on the 3.5mm jack
is working fine.
I tried several tricks and none seem to be working.

Asking if anyone has such experience?  Any tip/pointer is much appreciated.
Thanks

-Vincent