$url = 'https://domain.sharepoint.com/'
$ListTitle = 'List Name'
$folderName = 'Folder Name'

# Paths to SDK. Please verify location on your computer.
Add-Type -Path "c:Program FilesCommon Filesmicrosoft sharedWeb Server Extensions16ISAPIMicrosoft.SharePoint.Client.dll"
Add-Type -Path "c:Program FilesCommon Filesmicrosoft sharedWeb Server Extensions16ISAPIMicrosoft.SharePoint.Client.Runtime.dll"

# Login
$ctx=New-Object Microsoft.SharePoint.Client.ClientContext($Url)
$username = "myuser@domain.com"
$AdminPassword = "my password"
$password = ConvertTo-SecureString -string $AdminPassword -AsPlainText -Force
$ctx.Credentials = New-Object Microsoft.SharePoint.Client.SharePointOnlineCredentials($username, $password)

# Fetch list
$ll=$ctx.Web.Lists.GetByTitle($ListTitle)
$ctx.Load($ll)
$ctx.ExecuteQuery()

# Find folder
$folder = $ctx.Web.GetFolderByServerRelativeUrl($ctx.Web.ServerRelativeUrl + $listTitle + '/' + $folderName + '/')
$ctx.Load($folder)
$ctx.ExecuteQuery();

# Fetch items
$spQuery = New-Object Microsoft.SharePoint.Client.CamlQuery

## View XML
$qCommand = @"
<View Scope="RecursiveAll">
    <Query>
        <OrderBy><FieldRef Name='ID' Ascending='TRUE'/></OrderBy>
    </Query>
    <RowLimit Paged="TRUE">5000</RowLimit>
</View>
"@
## Page Position
$position = $null

## All Items
$allItems = @()
Do
{
    $spQuery.ListItemCollectionPosition = $position
    $spQuery.ViewXml = $qCommand
    ## Executing the query
    $spQuery.FolderServerRelativeUrl = $folder.ServerRelativeUrl
    $itemki = $ll.GetItems($spQuery)
    $ctx.Load($itemki)
    $ctx.ExecuteQuery()

    # Loop through all items
    $noOfObject = $itemki.Count
    for($j=0;$j -lt $itemki.Count ;$j++)
    {
        $itemki[$j].ResetRoleInheritance()
        if($j % 500 -eq 0) # Processing 500 items at a time.
        {
            $ctx.ExecuteQuery()
        }
    }
    $ctx.ExecuteQuery()

    ## Getting the position of the previous page
    $position = $itemki.ListItemCollectionPosition
    Write-Host $position.PagingInfo $position.TypeId

    # Adding current collection to the allItems collection
    $allItems += $itemki
}
# the position of the last page will be Null
Until($position -eq $null)