Since version 3.4.5 SVG vector graphics can be used as masks for views. Please note, that the SVG mask can currently only contain one path or combined paths, that will be used as a mask. To add a mask open the view you like to add it to in the product builder. Above the Canvas, click the "Edit mask" button:
A menu will open. To add a mask, click on the image icon.
In this example the used SVG is a svg with two combined paths. Only the intransparent area of your SVG is masked, the rest will be displayed - this applies to all content you have added or that the customer adds within that view.
Additional options in the mask menu allow scaling and positioning of the masking image.
If you want to use a background image or other content to be displayed in the rest of the canvas, you can upload a background image within the individual product settings.