The Last Guardian runs at 60 frames per second on the PS5, but only under some incredibly specific circumstances.
As you can see in the video below from Next Gen Base, GenDesign's superb game is able to achieve 60FPS on the PS5. However, as the narrator states, this is only possible if you're playing The Last Guardian through a disc, without any patches or updates installed.
The narrator states that they originally tested The Last Guardian on the PS5 through backwards compatibility, and it was locked to 30FPS. This was on a download format though, and they then saw a suggestion that 60FPS could be achieved if the game was played on a disc, without any patches or updates installed.
In short, they tried this method, and it proved to actually work. We can only assume that a post-launch patch for The Last Guardian locked the game's frame rate to 30FPS under all circumstances, so you'll need to avoid downloading any patches if you want the game to hit 60FPS on Sony's next-gen console.
Regardless, you should absolutely play The Last Guardian under any circumstances. No matter if it runs at 30 or 60FPS, it's without a doubt one of my favourite games of the last generation.
There are now just a few days until the PS5 launches, in the US at least. Due out on November 12 in the States, Sony's next-gen hardware will be launching exactly a week later on November 19 in the UK and Europe.