Trying to pop-out the instrument panels using AltGr crashes the game every time using DirectX12. It's fine with 11 but it tanks performance. It's about a 10fps hit with each popped out window.
Is one monitor HDR and the one you are trying to pop-out onto non-HDR? This caused me issues in the past. Disabling HDR on the HDR capable monitor allowed me to use the pop-out.