If you absolutely cannot afford a paid subscription, Avast One is your best bet. It provides decent core protection but lacks the advanced layers (Ransomware Rollback, Identity Insurance) found in paid suites.
Avast One Essential includes a file scanner, a basic firewall, and limited VPN usage (5GB/week). The interface is modern and friendly.
Free software isn't truly free. Avast will frequently show you pop-ups asking you to upgrade to the Premium version to unlock features like "Driver Updater" or "Sensitive Data Shield."