You seem to have understood the problem. But then you didn't follow. If there was a way to disable this, first thing that the grandma would do is watch a video how to disable that and lose security from then on.
Of course it is not perfect, but their approach here is really decent. And also, if you find yourself needing to go through that often I think that's not a good sign security-wise.
It's gone so far that even tech people now think that having root access to a mobile device is somehow scary. Well guess what that root access is still there for the manufacturer. It needs it for stuff like updates. It just shields you from having any kind of input or visibility on what is going on.
And once you've given up your admin control to the mega corporation, your government is going to be next. They'll be demanding backdoors and regulatory bullshit like age verification and snooping backdoors. Even today the EU launched yet another chatcontrol proposal. Eventually they'll manage to get it through when they've paid off enough representatives.
Keeping full control is the only way to prevent this.
My grandma absolutely would not watch and follow a video on how to e.g. disable Gatekeeper, nor do I think she’d be able to if she tried.
Your grandma sounds substantially more tech savvy than my grandma. Good for her, she seems to know what she wants. Grown adults should be allowed to knowingly opt into an additional level of risk.