Different screen times for different devices - Loosing my patience

Situation

My son has an iPhone on which I have setup screen time. It works fine, I can limit him playing games all day or watching videos. On his phone, I have checked off the option to share the settings across devices.

He's going to a new school, that required him to use an iPad. The (pretty tight) restrictions I had for his iPhone, don't need to be on his iPad (example; I have his phone pretty much locked during school hours), but he obviously needs to use his iPad. I Also checked off the option to share settings across devices on the iPad.

Even with the share settings option toggled off, it just keeps syncing all settings between devices (I've tried using workarounds with time limits). It's absolutely maddening.

I really just want to achieve one, very simple thing. Keep screen time settings on the iPhone, and no settings (or a completely different time schedule) on the iPad.

I can't really use the iPad without his iCloud account, because it's connected to his school account.

In hopes somebody can help me out, because I feel I've tried everything.