Take another look at the link I posted in my post #3.
That guy had a EFI partition, like you. He installed Debian, like you.
He found that a bootloader was not installed, like you.
He was trying to dual boot Windows, like you.
He spent a lot of time but was good enough to publish his solution.
Here's another link you may find useful:
Managing EFI Boot Loaders for Linux: EFI Boot Loader Installation