Is it possible to know who invited external users in SharePoint online sites, files, etc? Once the external account has been created, I cannot see any way to know that, unless I am missing something.
Yo can go to Site Settings -> Access requests and invitations -> Show History. Here you will see 5 columns named Person, Permission, Requested On, Status and Request For. In Status Column Accepted by "SomeName" will be your invitee or approver.