So basically a battle royale that people don't take too seriously?

Nope. Battle royales are competitive, and therefore, bring a competitive playerbase.

Battle royales are always fun in their early days, but end up in a mess of sweats that turn the more casual players away.

......you could always try fall guys, though it doesn't have any resemblance to fortnite, and is the only one I can think of that isn't filled with sweats to the brim.