SharePoint Online: PowerShell to Change Access Request Email for All Sites

Requirement: Change Access Request Email in SharePoint Online.

PowerShell to Change Access Request Email in SharePoint Online for a Site Collection:
Lets set access request email for a SharePoint Online site collection using PowerShell.

#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"

#Function to call a non-generic method Load
Function Invoke-LoadMethod() {
   param([Microsoft.SharePoint.Client.ClientObject]$Object = $(throw "Please provide a Client Object"),[string]$PropertyName) 
   $ctx = $Object.Context
   $load = [Microsoft.SharePoint.Client.ClientContext].GetMethod("Load") 
   $type = $Object.GetType()
   $clientLoad = $load.MakeGenericMethod($type)  
   $Parameter = [System.Linq.Expressions.Expression]::Parameter(($type), $type.Name)
   $Expression = [System.Linq.Expressions.Expression]::Lambda([System.Linq.Expressions.Expression]::Convert([System.Linq.Expressions.Expression]::PropertyOrField($Parameter,$PropertyName),[System.Object] ), $($Parameter))
   $ExpressionArray = [System.Array]::CreateInstance($Expression.GetType(), 1)
   $ExpressionArray.SetValue($Expression, 0)
   $clientLoad.Invoke($ctx,@($Object,$ExpressionArray))
}

Function Set-SPOAccessRequestEmail([String]$SiteURL, [String]$AccessReqEmail)
{  
    Try{
        #Setup the context
        $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
        $Ctx.Credentials = $Credentials

        #Get the Web and Sub Sites
        $Web = $Ctx.Web
        $Ctx.Load($Web)
        $Ctx.Load($web.AllProperties)
        $Ctx.Load($Web.Webs)
        $Ctx.ExecuteQuery()
 
        #Check if the web has unique permissions
        Invoke-LoadMethod -Object $Web -PropertyName "HasUniqueRoleAssignments"
        $Ctx.ExecuteQuery()

        If($Web.HasUniqueRoleAssignments -eq $true)
        {
            #Set Access request Email
            $Web.RequestAccessEmail = $AccessReqEmail
            $Web.Update()
            $Ctx.ExecuteQuery()
            Write-Host -f Green "Access Request Email Updated for the Site:" $($SiteURL)
        }
        Else
        {
            Write-Host -f Yellow "Site '$($SiteURL)' is inhering Permissions from the Parent"
        }

        #Iterate through each subsite of the current web
        ForEach ($Subweb in $Ctx.Web.Webs)
        {
            #Call the function recursively 
            Set-SPOAccessRequestEmail -SiteURL $Subweb.url -AccessReqEmail $AccessReqEmail
        }
    }
    Catch {
        write-host -f Red "Error Updating Access Request Email!" $_.Exception.Message
    }
}

#Set parameter values
$SiteURL="https://crescenttech.sharepoint.com"
$AccessReqEmail="Support@Crescenttech.com"

#Get Credentials to connect
$Cred= Get-Credential
$Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.Username, $Cred.Password)

#Call the function 
Set-SPOAccessRequestEmail -SiteURL $SiteURL -AccessReqEmail $AccessReqEmail

SharePoint Online: Change Access Request Email Address for All Sites in the Tenant

#Load SharePoint CSOM Assemblies
Add-Type -Path "C:\Program Files\SharePoint Online Management Shell\Microsoft.Online.SharePoint.PowerShell\Microsoft.SharePoint.Client.dll"
Add-Type -Path "C:\Program Files\SharePoint Online Management Shell\Microsoft.Online.SharePoint.PowerShell\Microsoft.SharePoint.Client.Runtime.dll"
Add-Type -Path "C:\Program Files\SharePoint Online Management Shell\Microsoft.Online.SharePoint.PowerShell\Microsoft.Online.SharePoint.Client.Tenant.dll"

#Function to call a non-generic method Load
Function Invoke-LoadMethod() {
   param([Microsoft.SharePoint.Client.ClientObject]$Object = $(throw "Please provide a Client Object"),[string]$PropertyName) 
   $ctx = $Object.Context
   $load = [Microsoft.SharePoint.Client.ClientContext].GetMethod("Load") 
   $type = $Object.GetType()
   $clientLoad = $load.MakeGenericMethod($type)  
   $Parameter = [System.Linq.Expressions.Expression]::Parameter(($type), $type.Name)
   $Expression = [System.Linq.Expressions.Expression]::Lambda([System.Linq.Expressions.Expression]::Convert([System.Linq.Expressions.Expression]::PropertyOrField($Parameter,$PropertyName),[System.Object] ), $($Parameter))
   $ExpressionArray = [System.Array]::CreateInstance($Expression.GetType(), 1)
   $ExpressionArray.SetValue($Expression, 0)
   $clientLoad.Invoke($ctx,@($Object,$ExpressionArray))
}

#Function to set access request Email of a site/site collection
Function Set-SPOAccessRequestEmail([String]$SiteURL, [String]$AccessReqEmail)
{  
    Try{
        #Setup the context
        $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($SiteURL)
        $Ctx.Credentials = $Credentials

        #Get the Web and Sub Sites
        $Web = $Ctx.Web
        $Ctx.Load($Web)
        $Ctx.Load($web.AllProperties)
        $Ctx.Load($Web.Webs)
        $Ctx.ExecuteQuery()
 
        #Check if the web has unique permissions
        Invoke-LoadMethod -Object $Web -PropertyName "HasUniqueRoleAssignments"
        $Ctx.ExecuteQuery()

        If($Web.HasUniqueRoleAssignments -eq $true)
        {
            #Set Access request Email
            $Web.RequestAccessEmail = $AccessReqEmail
            $Web.Update()
            $Ctx.ExecuteQuery()
            Write-Host -f Green "Access Request Email Updated for the Site:" $($SiteURL)
        }
        Else
        {
            Write-Host -f Yellow "Site '$($SiteURL)' is inhering Permissions from the Parent"
        }

        #Iterate through each subsite of the current web
        ForEach ($Subweb in $Ctx.Web.Webs)
        {
            #Call the function recursively 
            Set-SPOAccessRequestEmail -SiteURL $Subweb.url -AccessReqEmail $AccessReqEmail
        }
    }
    Catch {
        write-host -f Red "Error Updating Access Request Email!" $_.Exception.Message
    }
}

#Change Access Request Settings for All Site collections in the Tenant- Including Modern Team sites and communication sites
Function Change-SPOTenantAccessRequestEmail($AdminSiteURL)
{
    #Setup credentials to connect
    $Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($Cred.Username, $Cred.Password)
  
    #Setup the context
    $Ctx = New-Object Microsoft.SharePoint.Client.ClientContext($AdminSiteURL)
    $Ctx.Credentials = $Credentials
 
    #Get the tenant object 
    $Tenant = New-Object Microsoft.Online.SharePoint.TenantAdministration.Tenant($ctx)
 
    #Get All Site Collections
    $SiteCollections=$Tenant.GetSitePropertiesFromSharePoint(0,$true)
    $Ctx.Load($SiteCollections)
    $Ctx.ExecuteQuery()

    #Iterate through Each site collection
    ForEach($Site in $SiteCollections)
    {
        Set-SPOAccessRequestEmail -SiteUrl $Site.Url -AccessReqEmail $AccessReqEmail
    }
}
 
#Set global Parameters
$AdminSiteUrl = "https://crescenttech-admin.sharepoint.com"
$AccessReqEmail="Support@Crescenttech.com"

#Get Credentials to connect
$Cred= Get-Credential

#Call the function 
Change-SPOTenantAccessRequestEmail -AdminSiteURL $AdminSiteUrl

This changes access request email for all site collection in SharePoint Online.

Here is my another post to change access request email  or disable access request using PowerShell for a single SharePoint Online site: How to Change Access Request email or Disable Access Requests in SharePoint Online