Adaptive icons mandatory?

Just wondering if Android 8's new adaptive icons are REQUIRED and not optional for new apps. More specifically, I'd like to know what would happen if I left all of the Adaptive, Round, and Legacy icon fields empty in the player settings and only made use of the "Default Icon" Slot at the very top. This is my current method, and with the exception of the resulting squircle behind my actual icon, it seems to look just fine. Any known issues with just having a default icon?

 

I think API 26 is required now, and that wants adaptive icons, so yeah.

 

Ok. I have another question. For both adaptive and legacy icon tabs, there are 6 slots for different icon sizes. Must I make 6 different sizes for each slot? Because when I fill in one at the top, unity fills in all the rest automatically. However when I build the apk the icon turns out too big for the frame, therefore you can only see a portion of it.

 

I'm not sure. I tend to do it manually every time, so I can resize it with whatever algorithm I want, which is potentially better than whatever auto resizing Unity may do (although if it's Mitchell, it'll be pretty good).