Warning : file_get_contents

I got this after upgrading to D10 (from D9.4.8, module from 8.x-1.8-beta1 to 2.0.0-beta1 )

In my case the problem was the directory seemed to have moved ( libraries/datetimepicker -> libraries/jquery-datetimepicker)
After reading the README.MD properly my problem was solved using require "wikimedia/composer-merge-plugin":"^2.0" and adding the following to composer.json :

"extra": {
  "merge-plugin": {
    "include": [
      "[web-root]/modules/contrib/single_datetime/composer.libraries.json"
    ]
  },
}

Just leaving this for future reference.