So the footer is always at the bottom of the page, not at the window frame as no stick footer. Then there is content in the body and between the content and the footer there should be a div so wide/high that the footer at least touches the window frame.
You could use a grid system. Your footer would be in height "auto" and your content would be 1fr
.wrapper{
display: grid;
grid-template-rows: 1fr auto;
grid-template-columns: 1fr;
height: 80vh;
}<div class=wrapper>
<div>Content...</div>
<footer>Footer NEW</footer>
</div>