As part of Luma theme, the file

Magento/Catalog/view/frontend/templates/product/list/items.phtml

does provide a renderer for the various type of related products.

However, when deciding whether there is a content to display or not, slightly varied approaches are used.

Current implementation

a. for related items: if ($exist = $block->getItems()->getSize()) {
b. for upsell items: if ($exist = count($block->getItems())) {
c. for crosssell items: if ($exist = count($block->getItems())) {

Perhaps it is better to have a unified way, as for example that is done in the cases for related-rule, upsell-rule and crosssell-rule.

Related Pull Requests

#32778