Simple menu sometimes doesn't work when I click on it but other times it works...what could be wrong ?

https://ibb.co/F62BbXP

Also, the buttons on the top right(power, lock, etc) are low res on my monitor...but they are not low res in the picture...!! weird. Is there a way to increase their size ?

How about some more information about your distribution and exact Plasma version as well as graphic stack (card, driver)?

Also: no need to take pictures of a screen (those will be invariably blurry), just use the PrintScreen function, you will get better results...