How to Hide a Content Type from New Button Dropdown in SharePoint?

Requirement: Hide a Content Type from new button dropdown in SharePoint

How to Make a Content Type Hidden in SharePoint?
To hide a content type from new menu in SharePoint,

• Go to List Settings >> Under "Content Types", click on "Change new button order and default content type" link.
  
• Set the "Visible" flag to False by un-checking the tick mark. You can also change New Button Order.
  
  

This hides the content type in SharePoint.

SharePoint PowerShell to Hide a Content Type
We can also use PowerShell to hide a content type from the new menu in SharePoint.

Add-PSSnapin Microsoft.SharePoint.PowerShell -ErrorAction SilentlyContinue

#Set config variables
$WebURL="http://intranet.crescent.com/"
$ListName ="Projects"
$ContentTypeName="Project Template"

#Get Web and Objects
$Web = Get-SPWeb $WebURL
$List = $Web.Lists[$ListName]

#Get the content type
$ContentType = $List.ContentTypes[$ContentTypeName]
$ContentType.Hidden = $True
$ContentType.Update()

Write-Host "Content Type Hidden from the List!"

This hides the content type from the new menu dropdown.

SharePoint Online: Hide Content Type dropdown using PowerShell:
Similarly, in SharePoint Online to hide a content type we can use this PowerShell script.

#Load SharePoint CSOM Assemblies
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.dll"
Add-Type -Path "C:\Program Files\Common Files\Microsoft Shared\Web Server Extensions\16\ISAPI\Microsoft.SharePoint.Client.Runtime.dll"

#Config Parameters
$SiteURL="https://crescent.sharepoint.com"
$ListName="Contacts"
$ContentTypeName="Business Contacts"

Try {
    #Get Credentials to connect
    $Cred= Get-Credential

    #Setup the context
    $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
    $Ctx.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.Username, $Cred.Password)
        
    #Get the content type from the List
    $List = $Ctx.Web.Lists.GetByTitle($ListName)
    $Ctx.Load($List)
 
    #Get the content type from list
    $ContentTypeColl = $List.ContentTypes
    $Ctx.Load($ContentTypeColl)
    $Ctx.ExecuteQuery()
 
    #Get the content type to Hide
    $CType = $ContentTypeColl | Where {$_.Name -eq $ContentTypeName}
    If($CType -ne $Null)
    {
        $CType.Hidden=$True
        $CType.Update($False)
        $Ctx.ExecuteQuery()

        Write-host "Content Type is Set to Hidden!" -ForegroundColor Green
    }
    else
    {
        Write-host "Content Type Doesn't Exist!" -ForegroundColor Yellow
    }
}
Catch {
    write-host -f Red "Error Setting Conent Type to Hidden!" $_.Exception.Message
}

PnP PowerShell to Hide a Content Type in SharePoint Online List: 
Here is how to hide content type from the new dropdown in SharePoint Online.

$SiteURL = "https://crescent.sharepoint.com/sites/marketing"
$ListName = "Contacts"
$ContentTypeName ="Business Contacts V2"

#Connect to Pnp Online
Connect-PnPOnline -Url $SiteURL -UseWebLogin
 
#Get the Context
$Context = Get-PnPContext
 
#Get the content type from List
$ContentType = Get-PnPContentType -Identity $ContentTypeName -List $ListName
 
#Set content type to hidden
$ContentType.Hidden = $True
$ContentType.Update($False)
$Context.ExecuteQuery()