In TFS/VSTS there are different levels or group/permission settings:
Refer to Permissions and groups in VSTS and TFS for details.
You need to set them based on your requirements accordingly to make the system working as expected. That means you have to set them separately and for each team project individually. We cannot achieve that by simply set it only on Collection Level.
Default permissions and access for VSTS and TFS for your reference.
However in VSTS we can crate groups (eg: Developers
, Testers
...) and add users to the groups accordingly, also can add them to multiple projects during adding the users:
Manage Settings(gear icon) --> Users --> Add new users --> Enter the user eamil address --> select Access level --> Projects --> Add all --> set other options ... --> Add
