all my posts have a featured image that is also shown as the thumbnail in the posts’ archive page, but I want to replace it (just for the archive pages – category page showing blog posts, tag pages showing blog posts – all of them) with the value from a custom field, which has the image URL for each post

any idea on how to do this? I would need a function maybe (to add it on functions.php), something to force it, as editing the archive file is not really an option for me

I can’t seem to find anything like this on the internet or on this website

thanks a lot