MaxDeFa

After 3 weeks, I see there’s no support for this plugin ??

In your custom emplate – see the Template System instruction here: https://www.ads-software.com/plugins/list-category-posts/other_notes/ –
or in your default template
\wp-content\plugins\list-category-posts\templates\default.php

you must move this

//Post Thumbnail
  $lcp_display_output .= $this->get_thumbnail($single);

before this

//Show the title and link to the post:
  $lcp_display_output .= $this->get_post_title($single);

and then in the css of your theme you must add this:

.lcp_catlist img {
float: left;
margin-right:10px;
}

or this if you want also resize the thumbnails (for example 100×100):

.lcp_catlist img {
float: left;
margin-right:10px;
width:100px !important;
height:100px !important;
min-width:1% !important;
}

You could try to use !important in the css of your theme, like this:

.lcp_catlist img {
margin-right:10px;
width:16px !important;
height:16px !important;
min-width:1% !important;
}

And, if you want also move thumbnails on the leftside of the excerpt, use float, like this:

.lcp_catlist img {
float:left;
margin-right:10px;
width:16px !important;
height:16px !important;
min-width:1% !important;
}

As written here:
https://www.ads-software.com/support/topic/thumbnails-before-post-link?replies=3

You can create a custom template (instructions here Template System: https://www.ads-software.com/plugins/list-category-posts/other_notes/)
by copy this file
\wp-content\plugins\list-category-posts\templates\default.php

here (creating directory named list-category-post):
\wp-content\themes\my_current_theme\list-category-posts\

and renaming file from default.php to my_default.php

in this renamed file, move this

//Post Thumbnail
  $lcp_display_output .= $this->get_thumbnail($single);

before this

//Show the title and link to the post:
  $lcp_display_output .= $this->get_post_title($single);

and don’t foget to declare template name inside the shortcode
[catlist name=catname template=my_default]

if you want to move thumbnails on the leftside of the excerpt, use this code into css of your theme (change width and height with your custom dimensions):

.lcp_catlist img {
float: left;
margin-right:10px;
width:196px !important;
height:120px !important;
min-width:1% !important;
}

BTW, remember that you can also write a custom template instead of change default.php

instructions here: https://www.ads-software.com/plugins/list-category-posts/other_notes/ (Template System)

in the file
\wp-content\plugins\list-category-posts\templates\default.php

move this

//Post Thumbnail
  $lcp_display_output .= $this->get_thumbnail($single);

before this

//Show the title and link to the post:
  $lcp_display_output .= $this->get_post_title($single);