AFAIK turning it off as above will reset on a restart.
To permanently disable it is deliberately difficult. 10 Pro allows it but not on the simple settings above. To do it on non Pro you need to head into the registry (which you can do on Pro of course but it gives you an interface to set things where you are less likely to balls it all up.
You get what you ask for. MS was practically taken to court for not providing AV in their OS. I suspect the lawyers insist it isn’t easy to disable. Install another one and I’m pretty sure that kills it off.
They don’t want you to be able to not have an AV running......