Sections, including the home page, should have _index.md files instead of index.md files.
https://gohugo.io/content-management/page-bundles/
Example
content/
├── posts/
│ ├── post-1/
│ │ ├── a.jpg
│ │ ├── b.jpg
│ │ └── index.md <-- indicates leaf bundle
│ ├── _index.md <-- indicates branch bundle / section
│ ├── post-2.md
│ └── post-3.md
└── _index.md <-- home page