I see that from blueprint debug options you can launch the game in standalone and debug it. But is it possible to attach to an already running standalone and debug it? I could not find any information or option about that.
project is bp base or C++?
BP base. Would it be different if it were C++ base?
yes, with C++ you can attach/deattach external debuggers, but in BP you can’t do it , even if you do it in some cases it will be a pain 
As far as I know, the built-in Blueprint Debugger can’t attach to an already running standalone or packaged game. It only supports debugging sessions launched from the Editor.
This was one of the motivations behind Runtime Details. It lets you remotely attach to a running standalone or packaged game, use Blueprint breakpoints and step debugging, and inspect or even modify local and temporary variables at runtime.
