Qt has uic xml layout engine which was cumbersome to use, you weren’t discouraged from using c++ classes instead. The discouragement came later when Qt shifted towards qml (a bad shift as it’s just as unweildly, imo), now they discourage writing qml in c++ because the qml engine can get out of sync. Qt can prevent this but they want you to pay for a premium license for it. Slint is a sister to qt that does not have this restriction afaik.

I wish there would be an elegant c++ class/function based ui framework again.