No extra coding, just change some configs.

src-tauri/tauri.conf.json

{
  ...
  "app": {
    "windows": [
      {
        ...
        "zoomHotkeysEnabled": true
      }
    ],
  },
  ...
}

src-tauri/capabilities/default.json

{
  ...
  "permissions": [
    ...
    "core:webview:allow-set-webview-zoom"
  ]
}

This is a pretty new feature and not yet well documented in the official docs. The VS Code plugin and config schema can be helpful.