With the deprecation of Internet Explorer, it is currently no longer possible to install the Exchange Online Powershell module via ECP. But you can also install the Exchange Online Powershell module via Powershell itself:

First install the dependencies:

Install-PackageProvider -Name NuGet -Force
Install-Module -Name PowerShellGet -Force

Next install the Exchange Online Management module:

Install-Module -Name ExchangeOnlineManagement