A restricted member will not see a task unless it lives within a project that they have been granted access to.  For a detailed analysis of restricted member visibility, be sure to review the Access Rules for Restricted Members help article.

Inviting a person into your workspace as a restricted member 

You can set the restricted access level and specific project access right up front as part of the member invitation process. 

Converting an existing member to a restricted member

1. Go to settings > members & access control > member access
2. Select the appropriate workspace member on the left
3. On the right, choose the Restricted Member access level
4. Check the boxes to grant access to specific projects
5. Click Save