https://wccftech.com/fortnite-ps4-pro-resolution-bumped-1440p/

Epic Games released Update 6.10 for Fortnite yesterday. However, the developers don’t always make it easy to spot enhancements and fixes. For example, we’ve had to skim all over the official update notes to notice this one line regarding Fortnite PS4 Pro resolution.

If your PS4 Pro is plugged into a 4K TV, the game now renders at 1440p instead of 1080p.