Just some quick questions, are you playing on a monitor or a TV? is this the first time this happened? and if you go to the task manager is the process still running on the background?
Thank you for the quick reply. It is the first time it happened, I asked also on the Discord and somebody told me to Steam, right click on Lost Ark, and Properties → Local Files → Verify Integrity of game files. I just did that, and I was able to launch the game