I've tried building QtJSBSim with Qt 6.3, and it appears SVG handling has changed a bit, which prevents the current code from building. Rather than have two different code bases I've decided to not support a QT 6.3 version for now.
QtJSBSim builds with Qt 5.15.2
If I get demand for Qt 6.3, then I'll reconsider.
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I've tried building QtJSBSim with Qt 6.3, and it appears SVG handling has changed a bit, which prevents the current code from building. Rather than have two different code bases I've decided to not support a QT 6.3 version for now.
QtJSBSim builds with Qt 5.15.2
If I get demand for Qt 6.3, then I'll reconsider.