In all of Blizzard’s infinite wisdom, they removed the ability to find a group inside of their own game, because of some reason they piled out of a hat, idgaf.
Where can I go, what Discord server is there where I can find competent teammates?
There’s an official Overwatch discord server. Just google it.
Maybe try the subreddit. Also, they disabled the LFG feature because nobody used it. The few who did would break up the group after their first loss. It just wasn’t valuable.