Q: When I add someone to my workspace, can they see all projects associated with my workspace?
A: It depends on their workspace role.
Workspace Owner: yes, they have full visibility and access to every project in the workspace.
Workspace Manager: yes, Managers can see every project in the workspace regardless if they have been specifically invited. They can see the full project list from the Projects tab in Workspace Settings. Since they have full workspace access permissions, they can access the project or Delete it for all.
Workspace Editor: no, Workspace Editors only see projects they've been explicitly invited to.
New workspace members can be set to either role when you invite them and can always be changed or deleted from the Members tab in Workspace Settings.
Learn more: How to Add a Member to a Workspace You Own.