My material-ui version when first downloaded was an earlier version. Then i ran:

npm i -g npm-check-updates
ncu -u
npm install

to let it upgrade automatically to latest version.

I had to downgrade npm node@11.15.0 and npm install @material-ui/core@4.12.1 then it fixed all issues. Please check node version with your node.

You should update your package.json with following:

"@material-ui/lab": "4.0.0-alpha.57",
"@material-ui/pickers": "3.2.10",

I had the same problem with Skeleton using version @material-ui/lab": "4.0.0-alpha.60 but changing it to version @material-ui/lab": "4.0.0-alpha.57 fixed it for me ... guess they broke it again :)

Please try updating to latest version of @material-ui/core. That should fix the issue.

i can't solve this problem with above solutions.
so manually change 'alpha' to 'fade' in material ui files

./node_modules/@material_ui/lab/esm/

for example :

import { fade, withStyles, useTheme } from '@material-ui/core/styles';

instead

import { alpha, withStyles, useTheme } from '@material-ui/core/styles';

it's works for me
but it's not correct solutions.

update npm @material-ui/core package npm update resolved my issue

Maybe it'll be helpful for someone. For me fix of that issue was to change the indirect import to direct one:

so this triggered the error:

import { Alert } from '@material-ui/lab';

this works fine:

import Alert from '@material-ui/lab/Alert';

I was using MUI v4 and was trying to use the Appbar from MUI, updating my MUI by running the command npm install @material-ui/core@latest and restarting the server by using npm start worked for Me, Hope this helps!!