featured images not showing

Hi

I’m using half baked theme
I’m really liking the way it look
but unluckily it doesn’t show featured images of posts, that is really important to me, so I’m seeking for an help.
I’m not a developper, neither a very experienced used, so I tried my best adding a fonction in fonction.php

add_theme_support(‘post-thumbnails’, array(‘post’));

but it doesnt worked neither

the page where i would like featured images to show is:
https://www.lupeficara.info/?cat=5

and the following

https://www.lupeficara.info/?cat=27

being a peinter, images are the main content of my posts

can this issue become from the fact i organized posts under cathegories?

anyway thanks in advance for your help and attention.

LF