Fix WordPress Critical Error

I need help resolving a critical error on my WordPress website. I cannot access the admin dashboard at all.

Requirements:
- Diagnose and fix the critical error
- Restore full access to the WordPress admin dashboard
- No recent changes made to the site prior to the error

Ideal Skills and Experience:
- Strong experience with WordPress troubleshooting
- Familiarity with WordPress error logs and recovery modes
- Ability to work efficiently without needing to access the site’s admin panel

Please provide a brief outline of your approach and estimated time for resolution.