Yes, these changes apply to Primordial (in case you were wondering).
In short, here is the new Companion Rule: Once per game, any time you could cast a sorcery (during your main phase when the stack is empty), you can pay 3 generic mana to put your companion from your sideboard into your hand. This is a special action, not an activated ability.
You can find more details about this change on the official June 1, 2020 Banned and Restricted Announcement.
