Console warning: component lists rendered with v-for should have explicit keys

My solution to a similar problem looked like this:

- <el-radio v-for="option in field.options"> ...
+ <el-radio v-for="(option, index) in field.options" :key="index"> ...

Or using v-bind syntax for index:

+ <el-radio v-for="(option, index) in field.options" v-bind:key="index"> ...

The answer is listed explicitly in the documentation you linked...

<todo-item v-for="todoItem in todos"
           v-bind:data="todoItem"
           v-bind:key="todoItem.text"></todo-item>

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To summarise some information from the comments below... you use :key to let the component know how to identify individual elements. This allows it to keep track of changes for Vue's reactivity.

It's best to try and bind the :key to some uniquely identifying property of each item. For example, an id.