The sudden drop from 8000 to 400 indexed pages alongside zero new content indexing strongly suggests a manual penalty or significant algorithmic filter. Since you're in the crypto niche, Google is especially strict due to past abuse in this space.
First, check your Manual Actions report in the Search Console. If clean, review your content for potential E-E-A-T issues - crypto content needs to show clear expertise and authority. Make sure your authors have visible credentials and your site demonstrates trustworthiness.
I've seen similar cases where reducing posting frequency (from 40 to 10-15 quality pieces per day) and focusing on depth rather than quantity helped recover indexing. Also ensure you're not duplicating content from other crypto news sites, as that's a common trigger for indexing issues.
You might want to audit your backlink profile too - aggressive link-building in the crypto space can trigger filters.