Is there any built-in behavior for Command + Delete (delete line right of cursor) in macOS?
Apparently, macOS Supports Emacs style shortcuts...

What you are looking for is this: Control + K

Technically by holding the fn button with the backspace you get the actual Delete key, but on my mac at least it doesn't allow forward delete to the end of the line, but the above shortcut does.

This should work but doesn't:
fn + Command + Backspace

However you've got an answer now...

Source: Apple Questions