Front page showing ACF only once, is that solvable to show the ACF per post? [closed]

I think your fields still need to be placed inside the while loop, otherwise it will only show data for one post only. When the loop switches to the next article, it won’t execute your code ACF fields again as those are not currently inside the loop.

So try something like:

<?php get_header(); ?>
<div id="main">
<hr>
<div id="content">
    <?php
    if ( have_posts() ) {
        while ( have_posts() ) {
            the_post();
    ?>
    <?php $work_years = get_field('work_years'); ?>
    <?php $image = get_field('image'); ?>
    <?php $function = get_field('function'); ?>
    <?php $certificates = get_field('certificates'); ?>
    <?php $website_link = get_field('website_link'); ?>

    <?php include 'postinfo.php';?>

    <?php 
        }
    }else{
    ?>
      <p><?php _e('Sorry, no posts matched your criteria.'); ?></p>
    <?php
    }
    ?>
</div>

</div>
<div id="delimiter">
</div>
<?php get_footer(); ?>

And the postinfo.php would be:

<?php echo $work_years; ?><br />
<img src="https://wordpress.stackexchange.com/questions/288051/<?php echo $image; ?>"><br />
<?php echo $function; ?><br />
<?php echo $certificates; ?><br />
<a href="<?php echo $website_link;?>">Website</a><br />

<h1><?php the_title(); ?></h1>
<h4>Posted on <?php the_time('F jS, Y') ?></h4>
<p><?php the_content(__('(more...)')); ?></p>
<hr>

BTW, I don’t follow why you introduced the file postinfo.php and not have that code all in the first file alone. However, I suppose you got your reasons based on your site.