As of now (Oct 16, 2022) the last release is 1.5 years old (2.1.0 from march 29, 2021).
It supports Qt until version 6.0, while current version is 6.4. There are known issues and a patch for Qt 6.2 (see https://www.qcustomplot.com/index.php/support/forum/2380) but I did not get it working for Qt 6.3.
Is QCustomPlot still maintained?
Or should I consider using Qt's own QChartView for new projects?