Hi
Do you mean that redirecting to the home page is not good practise(SEO) and the 404 should be shown instead?
Yes, absolutely.
You should 100% redirect 404s,
but only if the target page are similar.
If the 404s simply are gone and don't have any pages on the new site that are on the same topic or bring information about that content, then the most SEO efficient thing to do is to tell search engines to remove them from their index, and you do that by letting them be 404.
You don't gain anything by redirecting pages to
unrelated new page (such as the homepage),because search engines will not transfer ranking to that new page (because it's not similar to the old one). And so you're wasting your crawl budget for instance.
This is why the standard sh404SEF 404 error page display is designed to offer similar urls to your visitors, and in any case keep them on your site, even if their bookmarked page is gone.
Rgds