Honestly this is so convoluted and needs an overhaul. It should be a lot simpler to add people you’ve just played especially.
Why is is buried in Click More → Frenemies → Manage → Add frenemies → Search their name and then send add.
So it’s weird that there’s no ‘search or add’ on the frenemies page, having to go to Manage, and by the time you get there you still have to remember the correct spelling of some odd names, and back out again if you don’t. It shouldn’t be under More anyway but under profile, next to past games.
Ideally there should be an add button or click on name to add, which would be much easier. Probably on the match result page.
You could secondary add how many times you’ve played that person and the win/loss ratio, like chess, to boost the rivalry.