How have Friendship and Affection changed in Sword and Shield?

My Eevee evolved into a Sylveon even though I never played with it in Pokémon Camp. Assuming camp was a replacement for amie/refresh, this should not be possible.

How has friendship and affection changed?

Friendship and Affection have been combined in Sword and Shield. (Let's just call it happiness for this post.)

Happiness is gained in the usual ways as before, such as levelling up, walking around, eating certain berries, and so on, but it is capped at 160. To get a higher happiness than this, Camp (and eating curry) is required.

The in-battle bonuses (such as increased crit chance, increased experience gain, and so on) are only obtained once the happiness is higher than 160, so if you never play with your pokémon in Camp, you will never receive these bonuses.

On the other hand, any pokémon that needed high friendship to evolve will require playing with them in Camp, as they now evolve at 220 happiness. (Sylveon used to require "two hearts" of affection to evolve in previous games, which has been changed to requiring 160 happiness.)

If the in-battle bonuses are not desired on a pokémon that evolves this way, you will have to decrease its happiness after it evolves through things like letting it faint or feeding it herbal medicine.