I have added firstname.lastname@example.org as guest user in Azure Active Directory but I cannot find this user in the office admin center or at powerapps to share the powerapp with email@example.com, Please help.
Please see below screens
Added the user in AZURE AD ,in Enterprise Application as well.
Can you share more details on Modern Driven Apps ?
and do you say that this is why you can not add guest users for powerapps?