You are using a non-X11 window system (e.g. Wayland) which is currently not supported by SimpleScreenRecorder. Several features will most likely not work properly. In order to solve this, you should log out, choose a X11/Xorg session at the login screen, and then log back in.
how fix error?
The best would be to report this problem upstream that the Devs. from SimpleScreenRecorder will make it wayland compatible.
Alternative, till the app is compatible you can reinstall x11, what is not installed by default anymore in KDE.
Not a fix for simplescreenrecorder, but OBS Studio can record screens/displays no problem Wayland/Xorg
can all record on Wayland.
simplescreenrecorder is X11-only, this is expected