That logo is generally the favicon for the website. Looking at the source code, I can see one is there, but it may have been cached if you’ve only just added it. When I first visited the site, I saw the default Silverstripe icon, and had to do a hard refresh to get it to change.
rel=“shortcut icon” is a legacy value. The standard now is just rel=“icon”
The image you’re using is over 1000px. You’d be much better off with a smaller, simpler version.
The file type is wrong for a favicon — type=“image/x-icon” is for .ico files, but you’re pointing to a .png. For a PNG favicon, use image/png.
Have a search for favicon generators online. There are plenty which will convert your files to the best formats, and give you proper markup to use them.