No comment on Nikon, I am a Canon user and don't know Nikon well.
The Target sale Canon T6 Rebel with 18-55mm and 75-300mm would be a great bet for "new" camera. It does allow for full manual operation, as well as program, aperture-dominant, shutter speed-dominant modes. Although the camera was released in 2016, it has a 2010 sensor (same as 60D and 7D) and doesn't have some of the more sophisticated video features of the others in the T6 Rebel family (which are more expensive). The camera DOES have Wi-Fi, if that's of interest. Lenses are "good enough", older kit lenses, fine for beginner. This is actually a decent bargain kit.
Canon 60D is a nice alternative to a Rebel, for those who find the Rebel a bit too small for their hands. There are several used ones with kit lens under USD 500.00 on Ebay now. If he wants to shoot sports or wildlife, the used Canon 7D is now about the same price. I'd probably get the 7D. These are good cameras, about 8 to 10 years from release. Stock it with a Canon 18-55 mm EF-S lens, STM focusing if he is interested in video, standard USM focusing if he likes manual (because all STM focusing is by wire). Later on, he could get one of the 55-200 or 75-300 zooms used for cheap..
I love my 60D, and it is very amenable to manual use, as is the 7D. 60D has swing-out flippy screen for video convenience, 7D doesn't, but 7D has better (and more customizable) autofocus, a "joystick" control for autofocus points, a few more customizable buttons, and is built like a tank. You could get a used 7D or 60D, a used 18-55mm EF-S lens, a memory card or two, and a card reader (if his computer doesn't have one) for USD 500.00, and the Canon RAW developer program (DPP) is free.