Looking at the Qt version history and Qt’s page on high DPI, it seems that possibly relevant functionality has been introduced in versions 5.6, 5.11 and 5.14.
Version 5.12 is the latest LTS, but will only be supported until December 2021. It seems that after v6 will be the only open source release receiving bug fixes.
I’m curious to hear more about your experiences with Qt. I’ve been looking into a potential move to v6, but my experience with Qt is fairly limited. What are the reasons for sticking to 5.6 or 5.8?