Pick the moments, not the chrome
A 3D icon is a statement, and an interface can only make so many before it turns into noise. The places they earn their keep are the ones where a screen has to do some persuading: an onboarding carousel, an empty state, a paywall, a success moment, a permission request, a store screenshot.
The places they do not are the ones a person uses forty times a day. A tab bar, a toolbar, an overflow menu and a settings list all want line icons, because at that size and that frequency the reader wants recognition rather than decoration.
Sizes and density
Download the high resolution PNG and export the sizes you need from it, rather than scaling a small file up. On iOS that means 1x, 2x and 3x; on Android it means the mdpi through xxxhdpi ladder. Exporting each from the master keeps every density sharp.
Aim for 32 pixels and up in logical units. Below that the depth and the lighting stop being legible and the icon reads as a coloured shape, which is a worse outcome than a well drawn flat one.
Dark mode is where sets fall apart
Check every icon on your dark background before you ship. A transparent PNG has no background to clash, but an icon drawn with a lot of near white in it can disappear into a light theme or glare on a dark one, and you will only see it on the device.
The icons here are rendered with soft studio lighting and real shadow, which generally reads well on both. Generally is not always, so look at the actual screen. Every sitewide mistake of this kind on this project was made by somebody checking in light mode only.
The app icon is a different problem
None of these is a launcher icon, and it is worth saying plainly because it is the most common mismatch. A launcher icon is a specific format with a required square canvas, a safe zone, platform masking, and rules about padding that differ between iOS and Android. A transparent PNG dropped into that slot is rejected by App Store Connect and rendered on a black square by Android.
What these are good for is everything inside the app. If you do want a launcher icon built from one of these, composite it onto an opaque background at the exact size the platform asks for and leave the safe-zone margin, then test it on a real home screen rather than in a preview.
The other thing worth testing on a device is weight. An onboarding carousel with six full-resolution PNGs in it is a slow first launch, which is the one moment a person decides whether to keep the app.
