There is a huge difference beyond one being a trained police officer.
George Floyd wasn't threatening to kill anyone. George Floyd was already restrained with handcuffs.
Neely was threatening to kill someone that was agreed upon by everyone at the scene including if you watch the body cam videos 2 black people. Another black person who was helping Penny restrain Neely I'm guessing agreed as well. No one who was there seemed to think Neely was just some young kid trying to kill a black guy. Instead they saw him as taking down someone who was threatening to kill them.
Also no one had handcuffs to restrain Neely. You should watch the below video, it has the video of Neely being restrained and it has body cam videos of cops asking questions of passengers. They all tell basically the same story, 2 of them are clearly black and made it very clear that they considered Neely to be a threat.