Comment by mmozeiko

I don't know why Signal calls it "DRM" because the do not use DRM for this. Typically DRM means encryption & keys are involved (which is what Netflix & others are doing with Widevine or PlayReady).

All Signal does is just a simple Windows API call to exclude window from screen capture. SetWindowDisplayAffinity function with WDA_EXCLUDEFROMCAPTURE argument: https://learn.microsoft.com/en-us/windows/win32/api/winuser/...