Overview of the favicon option under the Theme settings
To personalize the appearance of your desktop browser tabs, you have the option to upload an icon image that will be displayed as an icon.
The first step is to create a square PNG image with your brand logo. The size can be 512x512, 192x192, or even as small as 32x32. A larger size like 512x512 will display better on phones and desktops.
Upload the PNG image to your Shopify Files library:
In the Theme Editor -> Theme settings -> Favicon, choose the image:
Save your settings to complete.