Autodesk uses it, e.g. for Maya and Eagle. Tableau. Some game engines use it for editor tooling, e.g. CryEngine.

In the open-source world: Krita, Scribus, Texmaker.

The Dolphin emulator [0] and Krita [1] are two that come to my mind.

[0] https://dolphin-emu.org

[1] https://krita.org/en/

There is a wiki page that lists some.

https://en.wikipedia.org/wiki/Category:Software_that_uses_Qt

This is going to be a very limited list though, for instance there are dozens of applications in my domain that use Qt, and none of them are on this list.

Allegorithmic Substance, Guitar Pro, https://en.wikipedia.org/wiki/Category:Software_that_uses_Qt ...

I mean, just run a `find Qt5Core.dll` on windows or `find QtCore` on mac and see what's using Qt on your machine

Don't know if it is big or not, but Andy Brice's Perfect Table Plan is made with C++ and Qt, and IIRC, it runs on both Windows and macOS. It's been around for a long time and sells fairly well, according to posts on his blog, successfulsoftware.net , which I have been reading for a while. The blog also has many good posts about desktop software product development and marketing. Also, he's pretty much a one-man show, except fr some things, which shows it can be done.

Not terribly big, but big enough: LibrePCB (https://librepcb.org/)

Big in line count but not user count: Professional (the REALLY expensive stuff) 3D modeling and electronic design automation (EDA) packages.

I believe Maya and OBS use it

VLC, TeamViewer, Google Earth, Maya, VirtualBox.

Telegram desktop client app, dropbox.

Qbittorrent, Nuke and probably a lot of others.

(Answering myself)

DaVinci Resolve

Wireshark