Create unordered list from custom field type entires separated by a comma

If I understood you correctly, this should be pretty straight forward:

$rawcontent = get_field("myfield");
$rawcontent = preg_replace("!</?p[^>]*>!", "", $rawcontent); // remove <p>
$all_links = preg_split("/\s*,\s*/", $rawcontent);
foreach($all_links as $link) {
    if(!trim($link)) continue;
    print "<li>$link</li>";
}

A comma certainly would work, but note that this would break if you had commas inside the link text (<a href="https://wordpress.stackexchange.com/questions/285760/...">hello, world</a>).
You could easily alter the preg_split line to split on other things, though, like line breaks (\n). I’m not sure what the ACF editor inserts when you just press enter, but I’m sure that you can split it.