The option to provide a favicon for the self-hosted matomo installation is very good, but it is still missing different favicon sizes to be displayed properly on every operating system. For example, I added my matomo link to my favorites in macOS and iOS, but it isn't using the favicon as an icon.
Generating different sizes for favicons would be a great improvement. See this site for an example of the different favicon sizes: https://www.favicon-generator.org
I think nowadays every browser should support a simple single PNG file that is high resolution enough as a favicon and scale it to the size it needs.
I think the issue is just that Matomo resizes the favicon image to 32x32px on upload which might be a bit small.
I guess just increasing that number should improve the situation already a lot (especially as the default Matomo favicon is 256x256px)
But one would also need to update the resizing logic below to never upscale icons.
Guess it makes sense to simply generate a bigger one 👍