https://www.gamespot.com/articles/fortnite-playground-mode-remains-down-as-epic-shar/1100-6460056/

Update 4: Playground mode is still unavailable a day after it was set to return. Epic says progress is being made but it's trying to avoid rushing into pushing it up. "We're continuing testing on our matchmaking improvements and are still aiming to open the Playground LTM as soon as we're confident in our improvements," it said on Reddit. "Once we have confirmed that our testing was successful we will begin gradually rolling servers out to all regions and platforms until it's available to all players."

Meanwhile, another of the current limited-time modes is being replaced by 50v50, but the rollout of that has likewise been halted due to issues. We'll report back as we learn more.