I'm new to Linux and want to understand if X11 is really as dangerous as they say on the Internet?
I will explain how I understand this. Any application launched from under the current user has access to the keyboard, mouse, display (screenshot), and this is not good. BUT, if we install programs from the official repository (for example, for Debian), which are unlikely to contain keyloggers, etc., then the danger problem is clearly exaggerated. I am wrong?
Yes, you can open applications on separate servers (for example, Xephyr), but this is inconvenient, since there is no shared clipboard. Creating a clipboard based on tmp files is also inconvenient.