You can exchange Pokemon Go Friend Codes with more than 350k players on PokemonGoFriends Reddit.
https://www.reddit.com/r/PokemonGoFriends/
For those who want to know more about the Friends feature and how to add Friends, please see this link https://www.futuregamereleases.com/2021/03/pokemon-go-friend-codes-2021-exchange-friend-codes-with-more-than-250000-trainers/
Don't feel discouraged to add share each other's friend codes here. It's far better than sharing it in the comments section on the website.