This look like a Samsung Internet bug, though I don't really know what they're doing. This is the PWA installed from Samsung Internet and Chrome:
View attachment 240110
The icon in my case doesn't look as bad as the original screenshot, though it's clearly much worse than Chrome's (and doesn't appear to use the masking option).
I don't think there's really anything we can do about this. We define the icons (192x192 and 512x512) in the manifest and then it's up to the browser to choose how it uses them. It's possible that there's some really bad downsampling being done here, for example.