If you plan to keep using this Mac for another two years, you should look into (advanced users only) to upgrade to a newer macOS, or simply accept that the browser is your new permanent home.
Safari on macOS 10.15.7 does not natively support "Add to Dock" (a feature introduced in macOS Sonoma), so Chrome or Brave is recommended if you want the app-like feel. 4. Troubleshooting Common Issues on 10.15.7 "Browser Not Supported" whatsapp web mac os 10.15.7
Have you successfully set up WhatsApp Web on your Catalina Mac? Let us know in the comments below (or share your experience via a linked device!). If you plan to keep using this Mac