@Riz, this is not natively supported in Anthias yet.
TL;DR: Having two displays as one is not supported at the moment.
Out of the box, its possible only when duplicating displays, but with some catch. I tried connecting my Pi 4 to two displays: (1) FHD monitor, (2) 4K monitor. After the device boots up, display #1 shows the content at full size, while #2 (the larger display) shows the content with size similar to that of #1. If you’re using 2 displays of the same size, you’ll be fine.