
I did some further investigation using the sample application provided by the WebView2 team and was able to reproduce the issue there as well.
In their sample, the custom context‑menu icons are only 48×48. MSA, by contrast, uses proper multi‑resolution icon files containing several sizes. My understanding is that this is the correct and recommended approach, especially for handling different DPI and text‑scaling settings across monitors. It also used to work correctly in MSA, which strongly suggests that something has changed—or broken—in WebView2 itself.
I’ve reported my findings and am now waiting for official feedback from Microsoft.