Hello,

you should modify the access rule "Project/Task: employees: follow required for follower-only projects". 

Something like:

<record model="ir.rule" id="project.task_visibility_rule">

        <field name="name">Project/Task: employees: follow required for follower-only projects</field>

        <field name="model_id" ref="project.model_project_task"/>

        <field name="domain_force">[

        '|',

            ('project_id.privacy_visibility', '!=', 'followers'),

            '|','|',

                ('project_id.message_partner_ids', 'in', [user.partner_id.id]),

                '&amp;', <!-- And operator -->
                    ('user_id', '=', False), <!-- no user-->
                    (len('project_id.message_partner_ids'), '=', 0), <!-- NO FOLLOWERS-->
                '|',

                    ('message_partner_ids', 'in', [user.partner_id.id]),

                    ('user_id', '=', user.id)

  

        ]</field>

        <field name="groups" eval="[(4,ref('base.group_user'))]"/>

    </record>