The HTC U11+ was released over eighteen months ago and has yet to receive a single major OS update. In fact, the company's 2018 flagship, the U12+, hasn't received a major update either. The Taiwanese company has finally published concrete information on its plans to update those devices, though.
https://www.notebookcheck.net/The-HTC-U11-U11-and-U12-are-finally-set-to-receive-Android-Pie.420466.0.html