Issue

You navigate to SharePoint List -> List Settings -> Scroll down to content types -> Open a content type

Click delete this content type and receive the following error message:

Solution

The error message means that somewhere out there there are still items using that content type you are trying to delete. There are several ways you can fix it:

User Interface (Browser)
PNP Powershell
CSOM + Powershell
REST API

User Interface (Browser)

Step 1. Navigate to the list. Modify the view:

Step 2. Include Content type column:

Step 3. Save the view.

Step 4. In the list click on the content type column and select the content type you are about to delete.

Step 6. Either delete the items or change their content type under properties.

Powershell

Powershell is a better choice if you don’t know in which list the content type is being used and there is a lot of them. Powershell allows you to scan through multiple lists quickly.

With content type name

Content type name is easier because you already know the name of your content type. However, if there is a chance that you may have 2 different content types with the same name, you should be using the script with content type id, not name. For a script with content type id, scroll below.

# Specify your site and your client ID
Connect-PnPOnline -Url "https://acco967.sharepoint.com/sites/EWZ" -Interactive  -ClientId 00000000-4ead-4642-93a9-0000000000    

# Specify the name of your content type
$ContentTypeName = "MyCustomComment"   

# Get all lists in the site
$lists = Get-PnPList

# Initialize results
$results = @()

foreach ($list in $lists) {
    # Skip hidden or system lists
    if ($list.Hidden) { 
        continue
    }

    # Get items in the list with the specified content type
    $items = Get-PnPListItem -List $list.Title -Query "<View><Query><Where><Eq><FieldRef Name='ContentType' /><Value Type='Computed'>$ContentTypeName</Value></Eq></Where></Query></View>" -PageSize 1000

    # Count the items and get their URLs
    $count = $items.Count
    if ($count -gt 0) {
        $itemUrls = $items | ForEach-Object {
            "$($_.FieldValues.FileRef)"
        }

        # Add the results to the output
        $results += [PSCustomObject]@{
            ListName  = $list.Title
            ItemCount = $count
            ItemUrls  = $itemUrls -join ", "
        }
    }
}

# Display the results
if ($results.Count -eq 0) {
    Write-Output "No items with content type '$ContentTypeName' found."
} else {
    $results | Format-Table -AutoSize
}

# Optionally export the results to a CSV file
$results | Export-Csv -Path "ContentTypeReport.csv" 

# Disconnect from SharePoint
Disconnect-PnPOnline

With content type id

You can find content type ID using browser or Powershell.

# Connect to the SharePoint site
Connect-PnPOnline -Url "https://acco967.sharepoint.com/sites/EWZ" -Interactive  -ClientId 00000000-4ead-4642-93a9-0000000000    # Specify your site and your client ID

# Define the Content Type ID to search for
$ContentTypeId = "0x0101001234567890ABCDE"

# Get all lists in the site
$lists = Get-PnPList

# Initialize results
$results = @()

foreach ($list in $lists) {
    # Skip hidden or system lists
    if ($list.Hidden) { 
        continue
    }

    # Get items in the list with the specified content type
     $items = Get-PnPListItem -List $list.Title -Query "<View><Query><Where><BeginsWith><FieldRef Name='ContentTypeId' /><Value Type='Text'>$ContentTypeId</Value></BeginsWith></Where></Query></View>" -PageSize 1000

    # Count the items and get their URLs
    $count = $items.Count
    if ($count -gt 0) {
        $itemUrls = $items | ForEach-Object {
            "$($_.FieldValues.FileRef)"
        }

        # Add the results to the output
        $results += [PSCustomObject]@{
            ListName  = $list.Title
            ItemCount = $count
            ItemUrls  = $itemUrls -join ", "
        }
    }
}

# Display the results
if ($results.Count -eq 0) {
    Write-Output "No items with content type ID '$ContentTypeId' found."
} else {
    $results | Format-Table -AutoSize
}

# Optionally export the results to a CSV file
$results | Export-Csv -Path "ContentTypeReport.csv" 

# Disconnect from SharePoint
Disconnect-PnPOnline

Read Only

If your content type is read only, you need to change that setting first.

Navigate to:

Site settings
Site content types
Click on the name of the content type
Advanced settings
Should this content type be read only? Select NO

Content Type is still in use - How to remove stuck site content type