nginx 404 error?

Question

Nginx

404 is handled correctly if you go to site.com/adres404.html
i.e. at the end of .html,
if you go to site.com/adres404,
then it opens the main one (without any redirect)
in both cases, of course, there is no such page.
in nginx config
error_page 404 /404.html;
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what could be the problem is generally unclear. site in pure html.
before that, there were sites on the domains (i.e. drop domains) and Google indexed thousands of pages with one content. those. The search engine went through 404 and added everything to the index...