Hi
harishpathangay,
I'm sorry that your issue has yet to be resolved. But, as
PCNetSpec has stated,
there's a trillion things you could have done that are interfering with it, and only you know what you did prior to this occurring
I, personally, do not see anything suspicious in your posted information.
However, I think you
need to answer the question posed by
PCNetSpec:
...when you log onto the GUEST session pcmanfm isn't controlling the desktop (and yet whiskermenu is still slow) ?
Also, you
need to try the suggestions made by
PCNetSpec in his
Reply #14.

It
might be the solution, but
unless you try it we will
never know. Please try it and let us know if it helps.
Finally, in your
Reply #15 you state that
I am not Linux expert. I do have many DE installed.[Plasma,Gnome,Peppermint,XFCE,LxQt,Cinnamon,Mate]
I might suggest that given this situation, and if none of the suggestions made by
PCNetSpec help, you might only be able to solve this by re-installing the system.

I also personally believe that such large, complex
DEs (such as
Plasma,
Gnome, etc.) are
best used in
Linux distros that have been
designed from the start to work with them.
Peppermint Seven is a
hybrid that has been built and finely "tuned" to work
optimally with the
DE that is found when you do a fresh installation. It has
not been tested, designed and "tuned" to work (
optimally) with any of these other
DEs. It might, and probably will, work with them -- but not
optimally.
Regards,
-- Slim