It's been three months so I thought I'd give the 2020 software another chance (I been using 19.12.1). Well looks like they are still very buggy as of 20.3.1, I turned off toast notifications and loaded a game and what do you know, it showed the toast anyway. "Radeon Software - Press ALT + R to open"
Absolutely shameful incompetence, this should not be difficult at all. Even a child could write some software that checks a preference before doing something. AMD apparently cannot and simply ignores your settings.
Get your advertising off my screen AMD, I have no idea what you you were thinking when putting that there in the first place. When I have explicitly disabled that preference it should not even be possible for your software to show that toast under any circumstances. Get it right. There really is no excuse for this.