At SCL, domestic and international departures are in separate terminals which are not connected airside.

You would not be granted access to the international part (hence subject to clearing immigration and Security), where the excellent LATAM lounges are located, without holding a ticket for a flight outside of Chile.

Therefore, forget about LATAM lounge access on a domestic flight.

There is however an airport lounge which is open to holders of (local) credit cards and I think they also accept Priority Pass etc.. Personally, I have not been there in ages, but the place is smallish, often crowded and nothing to write home about.