@nminchin would a script like this work to set the windows full screen for you? It works to maximize a window to full screen mode (a second desktop, not a separate client) on two different monitors with different scaling on Windows 10 for me.
I should note the position recall on return to windowed state does not work well on the right monitor in a dual monitor setup with different scaling. It has the same issues as Designer windows that do weird stuff when switching between scaling on the monitors. But the swap to full screen mode works reliably filling the entire monitor on whichever monitor it is on.