That should not be a problem. You are right that eliminating those ingredients raises acidity so no further measures (like pressure canning) needed.

(I am assuming you are referring to a tested recipe with additional acid - i.e. vinegar or bottled lemon or lime juice.)

Carol

Standard tomato sauce canning instructions linked below. Nothing but tomatoes and lemon juice or citric acid.

Neither garlic nor onions are required for tomato sauce - ever. It is just tomatoes and lemon juice or citric acid.

For salsa, yes if you want a true salsa taste but if you want to call a mix of just tomatoes and peppers "salsa", that's your choice.

If what you want is Spaghetti Sauce (normally includes onions and garlic) then as Carol said you can just leave them out of the approved recipe but do NOT increase the amount of any of the other ingredients. Doing so changes the pH and the density.

Dave

Here is a link that might be useful: NCHFP - can tomato sauce