I have discovered a description of which platforms are (and by omission, which are not) supported by the maintainers of Qt. This may be found at Supported Platforms | Qt 5.15. While I have no doubt that @dismine is already familiar with this list, there may be others who, like myself, were not. I encourage anyone to be familiar with this list before becoming critical of quirky behavior that appears to be a malfunction in Valentina but is actually outside the control of the developer.