This was originally a comment on the question, but further googling has found some help.

One of my inherited projects has just started having this problem. 17:07:05:756 2025-09-29 17:07:05.712 -0400: WARNING: unknown:0 - SetProcessDpiAwarenessContext(DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2) failed: COM error 0x5: Access is denied.

(Double timestamp is due to me building in VS instead of Qt Creator, and VS's console adds its own timestamp. unknown:0 is because I think I don't have Qt debugging fully properly configured. If you can help, I'd appreciate it.)

This answer indicates that it's an ignorable error: https://forum.qt.io/post/738970

"As described in the documentation this error means that the DPI setting is already set at the point of this call."

Given that, I think this error has always been there, obscured by the noise of other errors. Clean-build-liness is next to build-godliness.