At the beginning, I saw How to get Site Owner Via Graph but unfortunately, it's not working as I would have expected.
I need to get primary admin for each and every site collection in my tenant. I need it to create a PowerApps app for my client to allow their employees to simply request access to SP sites in one place. I've already enumerated all sites, I have its SiteIDs, but the solution from the linked post is not working as expected. It's showing email address of site owner, but only for Team sites with "Group Owners" as primary admin. If any SP site has an individual account set as admin - flow is not listing it.
Most important thing - I need to authenticate via Azure App API - I can't authenticate by using any account, as I can't grant access to every site to technical account.