If you have Just Dance 2020 for example you won't be receiving any new songs from Just Dance 2021 and Just Dance 2022. If you have active Just Dance Unlimited subscription and you bought Just Dance 2022 your subscription will still be active even if you bought the new game. Additionally if you sign up with your Ubisoft Connect you will get 1 free month subscription.
Example: If you have 30 days of Unlimited and you linked your Ubisoft Connect account you will have 60 days of Unlimited.
If you have questions, don't hesitate to reply <3