Rename 0$ to Free

#1. First, you access Code Injection > Footer

#2. Enter below code then click Save

<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.0/jquery.min.js"></script>
<script>
$(document).ready(function(){
    $('.product-price:contains("0.00")').addClass('free-product');
});
</script>
<style>
.product-price.free-product {
    font-size: 0 !important;
}

.product-price.free-product:before {
    content: "Free";
    font-size: 18px !important;
}
</style>

#3. You will have results like the below

On List (Store, Category Page)

On Product Detail Page