虽然iOS 11.3支持Web应用程序清单，但尚不支持以这种方式指定图标.您需要将其包含在其他设备的清单中，但至少现在，您必须在iOS上使用以下内容:

While iOS 11.3 does support web app manifests, it does not yet support specifying icons this way. You'll want to include it in your manifest for other devices, but at least for now you'll have to use the following for iOS:

<link rel="apple-touch-icon" sizes="180x180" href="icon.png">

指定图标大小，并包括一个URL.

Specify the icon size, and include a URL.

在 Apple的文档此处了解更多信息

Learn more at Apple's documentation here

还有一个网站可以自动执行该过程在此处链接

There is also a website to automate the process linked here