Like where is the goto psych/CS UI 101 class/book/YT that over simplifies but grounds someone with no background or previous knowledge? Maybe something like the “Blender Doughnut” of great UI design?
I’ve changed UI twice with an app recently. I have a slight intuitive grasp of what I don’t like, but I lack the language and depth in this niche to express the emotional response well. I have no clue where to start with my own designs if I ever felt motivated to create one.
Speaking as a designer, it’s important to separate the style/trend of a UI from its function. I think what you’re looking for is actually UX design.
As a discipline, User Experience uses evidence-based research to understand how and why users behave they do. This leads to specific design patterns and principles that underlie all the good UI design seen from the giants like Apple, Google, Microsoft, etc. It gives you the language to evaluate designs. This is the foundation of your UI and the rest is just style — fonts, colors, imagery and icons which is subjective and less important. I lost ambition to be a trendy UI designer, so every design looks the same, but usability will shines through. Clean, simple and accessible is timeless.
Study the articles from nngroup.com. They pretty much established the field of UX Design, with content talking about user behavior in the 1990s. https://lawsofux.com is a more attractive and consumable option, also heavily influenced by NN Group. Finally, accessible design is good design for all, not just those with disabilities. Understand the guidelines set by the W3C for accessibility, like minimum font sizes or contrast ratios for colors.