How can I get the name of the user from their PC?

I want my game to breath the fourth wall, by getting the player’s name, using their name in their PC. Not the PC name, their actual name.

Is this even possible in GDevelop?

It’s not possible and this task is not as easy as it seems if you think about it more deeply. I would advice to discard this idea or use other engine if getting the PC data is a gonna be a core mechanic in your game.