Hi Subhabrata,
I am just a member here and have never answered any questions but just found your question when trying to solve the same issue for myself.
This may not help you, but I found that, in the customiser, (Customising – Layout – Blog):
I set the Featured Images Archives to use the Media attachment size (I use full, but you might use a thumbnail size), and then don’t set any size for the Width and Height (I had specified the width and height, so it was cropping width and making the height too big to make it fit).
Help article is at:
https://docs.generatepress.com/article/adjusting-the-featured-images/
Hope that helps,
Michael