Max Resolution /Windowed Issue, how was this released like this

I'm on an iMac pro with an external 43-inch UHD monitor.

Using just the internal AMD cards, the game will only allow the same resolution as the Retina display. Worse, it completely locks down the other display black so I can't even display a browser with guides or maps. With other games, I can glide my mouse right over to the other display without interrupting the game. Even in windowed mode. it assumes the shape of the retina resolution and can't be resized or maximized (maximize button is disabled) So I get a tiny window like 3/4th the size of my display.

So I bought an external GPU enclosure and another dual AMD Vega 64 card. I've cabled it to the enclosure so the only wire path to this monitor is thru the external video cards. Then I set is my primary display. It is the display I log into. It is the display my menu bar is located. It is the active display when I launch the game.
Nope. Same problem. It doesn't query the display number and then glean it's capabilities that way. Inside the game, it won't let me select the second AMD card.

I went into the options of the game and I specified eGPU... this actually results in a client crash.

This is a very easy and basic thing to do. Every other game I play on Mac, be it a native MacOS binary or run thru wine, it solves this problem. Literally after 1 chapter of "writing apps on macOS" you learn how you can do this.

It's a very cheap and easy fix. Please fix it. Interns are like $10 and hour and any sophomore comp sci or EE student could bang this out in 1 day, a week if they have zero macOS experience.

I can't continue with this horrendous display issue. How did a Mac version even get released like this?