The rootvalue function is not valid

When I used version 6.0.0, an error occurred,
In the vite + Vue framework, I want to use two different proportions for the UI framework
But in the end, all the documents used the ratio of 50
This problem was resolved when I tried to switch to version 5.1.1
`
postCssPxToRem({
rootValue({ file }) {
let num = file.includes('vant') ? 50 : 100
return num
},
propList: ['*'],
}),
`