I found that the Official Website of Material UI is using @material-ui and @mui.
But I find that If I use @material-ui or @mui Textfield, the UI doesn't works and the problems are mentioned below
React - Material label not in right position in Textfield
If you search Material UI in google, and go to https://mui.com/, it tells you to npm install @mui/material. But few weeks ago, I am using npm install @material-ui
If I have both @material-ui and @mui in my package.json, and I include both script and stylesheet in index.html, will there be any conflicts which mess up the UI
Update 1
In @mui CodeSandbox,
If you try Textfield with select prop, when you open the select, overflow: hidden will be added in body.

https://codesandbox.io/s/selecttextfields-material-demo-forked-z6b9f?file=/demo.js
In my project,
overflow: hidden; padding: 15px is added in body, but I checked I've done nothing about this!

material-ui version 1-4 are available on NPM under @material/core and versions >4 are available under @mui/material. Same library, but they changed the name in version 5.
Material ui has upgraded to V5 as per the recent tweet :https://twitter.com/MaterialUI/status/1438518915236126723?s=20
Since Sep 16, 2021 Material-UI changed his name to MUI to differentiate the company from Google. They say on the blog:
We are breaking the strong association with Material Design as we have seen too many people confusing Material-UI with Google, or as a synonym of Material Design.
Blog post here: https://mui.com/blog/material-ui-is-now-mui/
From version 5 the packages stored under @mui as you can found in documentation and you must use npm install @mui/material instead of @material-ui/core.