It's not the size of the tool icons that I want to change. Or the text size. I can manage these. It's other UI elements. See the image below.
1. This is the Foreground/Background color icon. It's size doesn't change like the other tool icons. The swap icon in it's upper right corner is so small it's almost impossible to click with the mouse.
2. The 'Transform' options (Layer/Path/Selection/Image) in the Unified Transform tool (other tools have the same icons). Very small. They can be enlarged a bit using the plugin cited earlier.
3. Checkboxes in tool settings. Too small to see the X if selected and hard to locate with the mouse. With a light theme, the checked boxes are dark and unchecked boxes are light, which is counterintuitive.
4. Paint brushes picker - these icons are also very small.
5. In the Layers pane, Lock option icons. Also very small.
These are examples of the UI elements that are very small on my 15.4", 3840 x 2160 laptop screen. They look fine at 1920 x 1080 (resolution of my desktop screen). I'm looking for a way to adjust these types of UI elements.