I'm wondering why Umbraco has removed the App_Data folder from the newer versions and where should I now add any data files that I use within the application. They shouldn't be in wwwroot Can I still add my own App_Data folder in the project or should I name it something else. It's for import files in this case, but may want to store temporary files in the future.

umbraco\Data

is where we put our stuff these days

You may use these to get the path of the data directory (and temp directory):

csharp
@using Microsoft.AspNetCore.Hosting
@using Umbraco.Cms.Core.Extensions
@using Umbraco.Cms.Core
@inject IWebHostEnvironment WebHostEnvironment

@{

    <h3>Data Directory</h3>
    <pre>@AppDomain.CurrentDomain.GetData("DataDirectory")</pre>
    <pre>@WebHostEnvironment.MapPathContentRoot(Constants.SystemDirectories.Data)</pre>

    <h3>TEMP Directory</h3>
    <pre>@WebHostEnvironment.MapPathContentRoot(Constants.SystemDirectories.TempData)</pre>

}

Umbraco sets the value for

@AppDomain.CurrentDomain.GetData("DataDirectory")

, so you can use that for getting the data directory - or use Umbraco's constant.

These are in the default

.gitignore

file by the way, so if you need to store data that should move accross environments you probably want to make your own directory for it.

I don't know if it changes the 'MapContentRoot' method. but the temp folder can be moved, and not actually be in the site folder at all (this is done when on azure, because the local temp folder is quicker than the disk that the site is on).

My example uses Umbraco's constants, so if doing that, I guess

MapPathContentRoot

will be incorrect