CheckoutWC works perfectly with Porto, but there is one setting that will create problems: Merge javascripts and stylesheets
You should not combine stylesheets and scripts. Before HTTP/2, this could increase performance but in modern times this will actually have the reverse effect. Modern browsers and servers allow browsers to process requests efficiently in parallel. Downloading multiple smaller files is faster than downloading a single big file.
How to Fix Broken JavaScript On The CheckoutWC Checkout Page With Porto Theme
Go to WP Admin > Porto > Speed Optimization Wizard > Advanced and uncheck Merge javascripts and stylesheets
Click Save & Continue
And now you’re done – the JavaScript errors that prevent the page from loading properly will be fixed.