Thank you for the suggestion, Unfortunately this seems to not quite work for the intended purpose,
I wanted to achieve the same, allow user to view a Project but inside that project only view the tasks that are assigned to him, and not other users tasks.

After following these suggested steps, the user will see the tasks under "My Tasks", however he will stop seeing the projects which have this visibility settings.

I did not manage to find an option of "Invite employees" as for what "invited employees" suggests, but the way I found was to send a following request to the project (which is really well hidden by pressing the follower/user button in the corner of the screen).
However this will show the entirety of the project to that user, so it defeats the purpose

Oh, I've noticed now that you specifically mentioned
"They cannot see the project, but they can see the tasks where they are"assignees"."

:) Nonetheless we will still need to search for an alternative

I understand your needs. I think this is not possible as standard.
Perhaps could be achieved with 'record-rules".
Good luck!