See steps below for joining a Session collaboration :
the Host user will notify you if you are added in the session as a participant
log off from your current VM session and re log-in. you will see a desktop session like this after logging in again, click the session boxed in blue to join :

after clicking that, you will see the desktop of the Host.
the Host user will notify you if you are added in the session as a participant
log off from your current VM session and re log-in. you will see a desktop session like this after logging in again, click the session boxed in blue to join :

after clicking that, you will see the desktop of the Host.
Published on: 26 / 04 / 2020