Magento 2 – Fix Error ‘Cannot Read Contents from File’ When Changing Themes

Deleting var/generation, var/cache and var/di solved it for me.

Maybe you have missing web and etc folder in your theme folder.

please add below code in your theme,

you need to copy entire web folder from /vendor/magento/theme-frontend-luma to app/design/frontend/Vendor/Theme/web folder

Also need to copy etc folder from default luma theme to your Vendor/Theme folder and check again

web folder is neccessary to add inside theme.

Now run command php bin/magento setup:upgrade

run deployment command, php bin/magento setup:static-content:deploy

Remove var folder and clear browser cache.

Set Your custom theme from

Content -> Design -> Configuration