The behavior you are experiencing, where the Chats section shows all users in the organization rather than just those you've had conversations with, may be related to the settings and policies configured in your new tenant. In Microsoft Teams, the visibility of users can be influenced by various factors including organizational policies, user roles, and tenant configurations.
If this is a new tenant, it's possible that the default settings for user visibility in chats differ from those in existing tenants. You may want to check the Teams admin center for any chat policies that might affect how users are displayed in the Chats section. Additionally, ensure that there are no specific settings that limit visibility to only those users with whom you've interacted previously.
For further assistance, reviewing the Teams documentation or reaching out to your IT administrator may provide more clarity on the specific configurations in your new tenant.