This is an example for the Upsell Product List :

Create the file app/design/frontend/Vendor/default/Magento_Catalog/templates/product/list/items.phtml

Line No. 62 and 82 replace below code:

 $limit = $block->getItemLimit('upsell');
 

to

 $limit = 3;
 

This is an example for the Upsell Product List :

Create the file app/design/frontend/Vendor/default/Magento_Catalog/templates/product/list/items.phtml

Line No. 62 replace below code:

$limit = $block->getPositionLimit();

$limit = 3;

and Line No. 82 replace below code:

 $limit = $block->getItemLimit('upsell'); 

$limit = 3;