Thanks a lot for the answer! I’m not entirely sure why these are the Qt rules -
If you use a QGC fork to build your own released version of QGC and your repo is not public then you need to have a commercial license of Qt. Those are Qt rules, not QGC rules.
Most of Qt is also licensed under LGPL 3 (see licensing), so in general software that uses those parts of Qt and can comply with that license can be released without the source code. That’s the main difference between GPL and LGPL, LGPL allows dynamic linking with Qt without affecting dependent code, as long as one does not modify Qt itself.
QGC for desktop links with Qt dynamically (the default), so I don’t see why one will not be able to comply with LGPL requirements. The only thing that does seem to prevent that is the dependency on Qt Charts (which is commercial / GPL only), but that can be disabled. I’m not sure about mobile platforms because dynamic linking may not be technically possible, but I’m only asking about desktop for now.
So if I may suggest alternate wording, I would remove the “commercial license required” phrase from QGC COPYING.md and instead direct users to the Qt licensing page while mentioning that Qt is either commercial or open source (GPL/LGPL). I would also mention that QGC uses Qt Charts which is commercial/GPL only to prevent any misunderstandings.