Things that have bitten me, roughly ordered by how much time they cost:

1. "no Qt platform plugin could be initialized" — the classic. Usually
   platforms/qwindows.dll missing, or present but in the wrong place, or built
   with a different kit than the exe.

2. QML app ships, launches, shows a blank window, logs nothing. Missing QML
   modules that windeployqt didn't collect because --qmldir wasn't right.

3. Every HTTPS request fails silently. Took me a while to find: Qt 6 needs the
   TLS backend plugin (qopensslbackend.dll / qschannelbackend.dll), and without
   it QNetworkAccessManager just returns generic errors with no clue why.

4. 0xc000007b on the customer machine. 32/64-bit mismatch, or a wrong-arch
   vcruntime140.dll already sitting somewhere in PATH.

5. Runs fine on my box, missing MSVC redistributable on theirs.

6. Antivirus flags the exe. Unsigned binary.

7. Fonts and widget styles look completely different on another machine —
   missing styles/ plugin.

My current process is: build, run windeployqt, then manually walk the deploy
folder against a checklist I've accumulated over years, then test on a clean VM.
It works, but it lives entirely in my head and it's easy to skip a step when
I'm in a hurry.

So, for those of you shipping Qt on Windows:

• Which of these have bitten you, and which one costs you the most time?
• What's the failure mode that is NOT on my list? I'm fairly sure I've just
  been lucky with a few.

Not selling anything here — I'm trying to figure out whether the checklist in
my head is a shared problem or just my own paranoia.