A new Graph API and the Teams AadSync process improve how Teams synchronizes group membership information with Azure AD. The older background sync process was tied to the Teams client and didn’t work so well in practice, especially when scaled up. Things look good for the new mechanism.
Microsoft revealed that Teams now supports a membership limit of 25,000 members per team (March 2021). The new maximum will help large organizations like Accenture (the largest user of Teams). Even with the increased limit, Teams might not be the best choice for organization-wide communications for the largest companies. Yammer is still the Microsoft collaboration scalability champ.