How to stop Mail popping up in split screen while I am using another app fullscreen?

While I am using an app in full screen, Mail will pop up and split the screen. This occurs every time an email is received.

For me, using apps full screen allows me to escape the clutter of windows on a desktop without multiple monitors. When another app pops up and splits my full screen, it defeats the purpose of the fullscreen feature the way I use it and I would like to turn it off. This is the most frustrating bug I have ever seen in a mac, and no software behavior has irritated me this much in a long time.

So far I have disabled:

"Prefer opening messages in split view when in full screen"

In the Mail preferences. Obviously this did not solve the problem. I'm not sure what that setting actually does but I left it off. I haven't found anything else related to Mail pop ups.

I also disabled Mail notifications entirely in System Preferences.

Is there a specific setting to shut down this intrusive and disruptive behavior from Mail?

Is there a third party pop up blocker that would work to silence Mail or another workaround to stop this?