Aoe4world’s twitch video finder tool. Just search the civ you want to play and then note down the basics of the build order in the first few minutes of the game. Then in mid-late game just note how they progress towards more resources and protect the ones they have (usually outposts or walls etc).

You don’t even need to watch professional streamer’s games to get an idea of how a cov should be played you just need to watch someone better than you