Unless things have changed I never paid Qt any attention because it is dually licensed and therefore not truly free software and its ownership keeps changing between commercial companies.
Last I checked Qt is "free" for open source projects but requires an expensive commercial license for anything else.
You last checked about a decade ago, then.
Here's how it works now (and has worked for a while now): Qt is Free. Not "free", but Free. It's under the LGPL. And the GPL.
"But it's owned by a commercial company, and they can just close off the source."
Nope. Still stays open. Back a few years ago, the KDE group got a special concession from Nokia. They set up the KDE Free Qt Foundation; if the commercial owners of Qt (Digia) stop releasing Qt under the LGPL and GPL3, KDE has the right to make the whole thing BSD. Irrevocably. And the agreement stays, even if Digia is sold, bought, etc. Read the link if you'd like to know more.
Basically, Qt is Free. If the owners ever stop releasing it for Free, KDE gets to release it under an even more Free license.
Qt has been Free for a while. Qt is still Free. It will remain Free