A server icon needs to remain recognisable among other small icons. A complex event poster or a long community name can become difficult to distinguish there. Use a compact logo, a clear initial, or a simple illustration that represents the server. The full name and description have their own places in the interface, so the icon does not need to repeat every detail.
This page prepares our 512×512 static PNG. The size is a chosen working export, not a claim that Discord accepts only that exact dimension. Check the current uploader and its preview when applying the file. Discord's server profile help explains the icon controls available to server administrators and owners.
Keep the central shape clear and leave enough room at the edges for the way the icon is displayed. A border or fine outer lettering may become difficult to see when the icon is small. Test the identity at that small size before investing effort in details that will not survive reduction.