Reading this thread, it appears that vector patterns still aren’t supported in Designer V2. Disappointing!
As an Illustrator user since version 1.0 – yes! I'm that old – and having worked as a designer at Aldus- the original owners of FreeHand – there are some basic concepts of vector drawing apps that I've grown up with. Being able to create and apply patterns within a document being one of those things.
I like to keep my designs live, and contain all the elements within one document. Having to export patterns as a PNG and then bring them back as a fill, is really clunky. I so wanted to fall in love with the new versions of these Affinity products, especially as the Shape Builder tool finally made an appearance in Designer. However it already feels like they're going to sit on my digital shelf for the next few years gathering dust.