Frozen Emacs-as-WM is usually a pending minibuffer prompt

When Emacs is also the window manager (EXWM-style setups), the UI can look hung while Emacs sits idle. Typical cause: a pending minibuffer prompt, e.g. after a file with a modified, locked buffer was deleted on disk. Signs are low CPU in ps and a .#file lock symlink next to the file. Try C-g, or answer or kill the buffer. If it still won't respond, pkill -USR2 -x emacs makes Emacs break out and enter the debugger without killing it, which matters when it owns the whole session.