I've upgraded to Hugo v0.20.5 and the generated file location of the index.md files changed. I don't think this was intended. Here is what happened:

I use following content structure to keep content and images together:

├── content
│   └── blog
│       ├── my-blog-post-1
│       │   └── index.md
│       │   └── image-for-post-1.jpg

This generates the following structure:

Hugo before v0.20 (expected behavior)

This is how it should be.

├── public
│   └── blog
│       ├── my-blog-post-1
│       │   └── index.html
│       │   └── image-for-post-1.jpg

Hugo v0.20 (wrong behavior)

├── public
│   └── blog
│       ├── my-blog-post-1
│       │   └── image-for-post-1.jpg
│       │   └── index
│       │       └── index.html

I think it is not intended behavior to have an additional index subfolder (/index/index.html).

There is a workaround if I set slug = '/' in the front matter but I would rather not do that.