Since the Articles Field Custom HTML Layout pertains to each individual article, it's a bit tricky if you wanted to display the linked articles in a bulleted or numbered list.

But it can be done. Starting from Joomla 3.9, you can create and assign alternate layouts for the rendering of a custom field, which makes it therefore possible to add any code around the output of the whole custom field.

So you could create an alternate layout file (for example called ordered-list.php) where you surround the field $value with <ul></ul> tags. Then, assign this layout to your custom field in "Options > Render Options > Layout".

Now, in the Articles Field Custom HTML Layout, you can simply surround the article output with <li></li> tags.

<li><a href="[url]">[title]</a></li>