SUMMARY
***
Okular opens too many X clients So I cannot start any other applications
***


STEPS TO REPRODUCE
1. open some document in okular, maybe using latexmk and work with it for a while
2. start hit any GUI program like xterm on a terminal window opened earlier.
3. You will see an error like
Maximum number of clients reachedxterm: Xt error: Can't open display: :0.0


OBSERVED RESULT
Maximum number of clients reachedxterm: Xt error: Can't open display: :0.0
Started GUI program crashes

EXPECTED RESULT
Started GUI program starts

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 20.04.4 LTS
Release:	20.04
Codename:	focal

KDE Plasma Version: / (using xfce and i3)
KDE Frameworks Version: /
Qt Version: 
$ qtdiag
Qt 5.9.7 (x86_64-little_endian-lp64 shared (dynamic) release build; by GCC 7.3.0) on "xcb" 
OS: Ubuntu 20.04.4 LTS [linux version 5.4.0-105-generic]

Architecture: x86_64; features: SSE2 SSE3 SSSE3 SSE4.1 SSE4.2 AVX AVX2 RTM HLE


ADDITIONAL INFORMATION

$ lsof -U | grep okular | wc -l
442

lsof -U +c 15 | cut -f1 -d' ' | sort | uniq -c | sort -rn | head -3
    442 okular
    310 dbus-daemon
    136 mattermost-desk