Maximum number of clients reachedqt.qpa.xcb: could not connect to display :0

I am using Linux Mint 20.1 Cinnamon with kernel version 5.4.0-97-generic. I am facing recent issue when try to open okular from terminal or start-menu..

Maximum number of clients reachedqt.qpa.xcb: could not connect to display :0
qt.qpa.plugin: Could not load the Qt platform plugin "xcb" in "" even though it was found.
This application failed to start because no Qt platform plugin could be initialized. Reinstalling the application may fix this problem.

Available platform plugins are: eglfs, linuxfb, minimal, minimalegl, offscreen, vnc, wayland-egl, wayland, wayland-xcomposite-egl, wayland-xcomposite-glx, xcb.

Aborted (core dumped)

There are many issues regarding this, but no particular solution were provided. Any help?