Find duplicate case insensitive filenames in all folders and sub-folders

I have about 250,000 files in several folders with sub-folders. Looking for a solution how to find duplicate filenames in all folders and their sub-folders. My OS is Ubuntu 22.04, using bash.

I prefer a bash command/script solution. However, suggestions about tools similar to fdupes -r (but checking if filenames are the same, not their content) are welcome too.

About the files and their names:

• All files are images and have file extensions.
• The content of the file is not important and may be different.
• The extensions of the files are not important and may be different.
• Letter casing for both file names and their extensions is not consistent.
• Some of the files have more than one . (period) in their filename. Example: file_Name2.1.png
• The file extensions are 3 or 4 symbols. Example: .png, .JPG, .jpeg

Structure:

The directory structure is pretty simple: ./[YEAR]/[MONTH]/[IMAGE_NAME].[EXTENSION]. For example:

tree -a
.
├── 2022
│   └── 12
│       ├── file1.png
│       └── File2.png
└── 2023
    ├── 01
    │   ├── file1.jpg
    │   ├── file3.png
    │   └── file4.png
    └── 02
        ├── FILE1.png
        ├── FILE4.PNG
        ├── File5.png
        └── File6.png

Expected result:

• file1:

  ./2022/12/file1.png
  ./2023/01/file1.jpg
  ./2023/02/FILE1.png
  

• file4:

  ./2023/01/file4.png
  ./2023/02/FILE4.PNG