This was opened by Darren Taylor on the Microsoft Graph UserVoice site and it did gather 19 votes there as can be seen https://web.archive.org/web/20201205153559/https://microsoftgraph.uservoice.com/...
Hello Edgar81. Have you been able to find a solution for this? We are trying to collect this data for ourselves as well. We tried powershell and GraphAPI to collect Teams conference data but cannot see any details at all for users from other tenants.