Hi Mateusz.b,
Thank you again for you help.
I managed to do it using labelFormatter only like I have mentioned in JSfiddle. I found the issue why it was not working when I was hovering over legends. The issue was with 'accessibility.js' . When I am using this JS, it is overlaying a button on top of Legend text and thats why when hovering tooltip was not showing up. I have also tested this without 'accessibility.js' there it is working fine.
Please check below jsfiddles
1) With 'accessibility.js' (This is not working) -
https://jsfiddle.net/Deokant/L7n2d1wb/
2) Without 'accessibility.js'(This is working) -
https://jsfiddle.net/Deokant/ne2x31f4/4/
But I can't use solution 2 as we are using 'accessibility.js' everywhere. So, to solve this I am using a workaround. When I am inspecting the legend element I see a button on top of legend text with class 'highcharts-a11y-proxy-button'. When I am hdding this button popup is working. So I wrote css to hide this class. I have tested the application after hidding this class and everything is working fine. Below is the work around fiddle
https://jsfiddle.net/Deokant/cpqsnbf1/4/
Thanks again for your help and support.