It is still very difficult to use Affinity Photo for mockups. However, I think a basic solution is to prepare layouts that allow you to use the perspective tool with ease. Also, leave prepared layers that can be used as masks.
On this, I would like to share something that I am working on:
In this template, I just import the business card's PNG images and adjust it with the perspective tool on one layer (hidden below).
The thickness and background colors are changed by selecting the desired color from the palette.
I'm currently revamping this model to insert a localized varnish mask.
See the result:
Seriously, this design took a long time to build, but to modify and use is super fast and easy.
I would like to hear from the community before proceeding to produce more Affinity Photo-specific mockups!