[Composite Alpha export to QuarkXPress]

Thank you Lagarto. I found one way around. Draw the mask with the Freehand Selection Tool, then Select > Save Selection > as spare channel.
Next: Document > Transparent background. Then export as: Tiff , Area: Whole document. This method works, different from Photoshop as I can't activate or deactivate the mask.

Attached two images

[Composite Alpha export to QuarkXPress]

Do Affinity Photo offer the same option as Adobe Photoshop to store composite Alpha channels that QuarkXPress can read. I use frequently the lasso tool to create alpha channels to isolate parts of an image (to isolate the background from an object). In Photoshop this is done under the Select menu. The mask is stored as a channel that you activate in QuarkXPress. I don't get it work in Affinity Photo.