Hey there!
A DLC called My First Pet Stuff is free to own forever.
As long as you claim a copy before 9th January 2024.
I’m not sure whether this is the true expiry date, or if this is an error. It’s a rather long freebie for an EA game, isn’t it? 
You will need The Sims 4 base game in your library first, which is free-to-play.
Teach your Sims how to care for smaller household pets, decorate a home with pet-inspired furniture, and dress pets in your favourite Sims outfits!
Have fun! 