ZorinOS. My elderly parents have been using it for years without any issues, so I can guarantee you that it's very noob-friendly.
However, if you'd like to game, I'd recommend using either Pop!_OS or Nobara instead. I'd recommend giving them all a try regardless, just create a bootable USB using Ventoy and chuck all the ISOs you wish to try.
Ubuntu Christian Edition, if he's a satanist.
Ubuntu Satanic Edition, if he's a Christian.
Hannah Montana Linux, if he's neither of the above.