Another vote here for “not too long” – she’s a Clyde, they’re supposed to be hairy!
My haflinger gelding has a silly, poofy-looking mane right now because somebody, bless their hearts, tried to pull his mane in English hunter fashion before I got him. The rest of his herd have long manes and forelocks in typical Haffie fashion. Some of them look like golden fairy-princess horses with how long their manes and tails are, and we ride and drive them like that! I think the only time we braid their manes out of the way is when we’re going to shows, and only then because it looks nicer.