A couple links from asus and microsoft just to make sure that something has not been overlooked.
https://www.asus.com/us/support/faq/1015070
https://answers.microsoft.com/en-us/windows/forum/all/asus-vivobook-15-audio-and-microphone-not-working/4ded75cc-05e9-46e6-948c-a45678906e3e
if the speaker inside just makes a fuzzy sound or rattles it may have a diaphragm failure. In that case, using external speakers should work and avoid repair cost. The mic and speaker may be on a sub board that can be easily replaced by a tech. If part is on main board, it may be time to look at a new model.