Hi @JollyGood97
Most definitely Microsoft Teams has a client-server architecture (as do all Microsoft cloud services). Furthermore, there are a wide range of cloud services (Azure AD, SharePoint, etc) and content delivery networks that act as backbone for providing you the full MS Teams experience. What I'm explaining is just the tip of the iceberg as you can find more information below to dive deeper.
Here is a good starter article on the front-end services of MS Teams:
http://communicationsknowledge.blogspot.com/2018/03/microsoft-teams-client-and-service.html
Microsoft Teams IT architecture and voice solutions posters
https://learn.microsoft.com/en-us/microsoftteams/teams-architecture-solutions-posters
Microsoft cloud for IT architects illustrations
Microsoft Teams Architecture Deep Dive Maarten Eekels (YouTube Video)
https://www.youtube.com/watch?v=qcpVbg1XIuE
TEAMS ARCHITECTURE FOR IT-PROS AND ARCHITECTS (Some good networking/app/foundational architecture)
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