Dynamax Pokémon and Max Battles were introduced in Pokémon Go in September 2024. Since then, a number of Dynamax Pokémon and Gigantamax Pokémon have been released. I've put together a Dynamax debut timeline for reference that might be helpful to see what you've missed if you've just started playing or haven't played in a while:
Here's a list of limited-time events and raids in Pokémon Go in the month of February 2025 (you can find a schedule of shorter hourly events in the calendar ):