During development, PUBG's developers worked closely with Epic for technical support of the Unreal Engine. At the time, Epic was developing a multiplayer sandbox game that focused on building fortifications and area defense. It was a little-known title called Fortnite.
PUBG launched into early access in March of 2017 and was an immediate massive success. Only half a year later, Epic launched Fortnite Battle Royale, which was a massive departure from the original Fortnite concept. It had the same genre as PUBG, it had the same game rules, the gameplay was nearly identical; and it retained barely anything from the original core gameplay loop of fortification-building. You'd have to be willfully ignorant on the level of flat earthers to think it's all just an innocent coincidence.
I don't think Epic directly stole any of PUBG's works, but I am absolutely certain beyond doubt that they took "inspiration" from PUBG the same way Richard Wagner took inspiration from Germanic mythology when writing his opera. Whatever abhorrent eldritch abomination Fortnite may be today, it started its life as a complete rip-off.