I am an engineer not an UI/UX designer. I dabble in those things and sometimes have an idea of what is good and bad from past experience but it is certainly not my strength. You can see that in the evolution of Monal over the past decade. We are always presented with a need to balance user friendliness with lots of options. I have rarely seen anything get the balance right. Oddly artwork has always been one of the hardest things to deal with.
Icons are super important. I started off using icons from KDE and later bought Glyphish, which I have been using since iOS 5 or so. I recently discovered Icon Deposit, where a lot of things I would have killed for in the past are available for free with attribution. It is the open source model applied to artwork. This is something I would recommend other developers checkout. Are there other resources like this? I haven’t paid attention to it in ages.