The issue you’re being flagged on is the Total DOM Elements of 1449. ( the doc above states its an issue at 1500 – but its out of date – see here )
The maximum DOM Depth only gets flagged if it reaches 32. And the Element it lists is just the deepest nested element – that itself is not a problem and not anyway to related to that Diagnostic report being flagged as red.
Simple explanation of DOM Elements.
Every element – ie. text block, image, advert or other HTML you add to a post gets counted as DOM element. The only way to reduce that is to remove content from the page, or use Page Breaks to paginate the posts.
But its only a diganostic and has no direct effect on page speed scores – it only becomes a problem is you’re using a lot oF CSS or JS on your page to create the layout. More DOM Elements * More code = greater processing time for the browser. If this were an issue you would most likely see CLS issues or poor rendering of the site when it is viewed.