It may have taken over 7 months, but HTC has finally confirmed in which quarter it plans to release Android 9 Pie for the U11, U11+ and the U12+. The three devices should receive the update in Q2 this year, which could by the end of June at the latest. Do not hold your breath though, because HTC has thrown in some caveats too.
https://www.notebookcheck.net/HTC-could-release-Android-9-Pie-for-the-U11-U11-and-U12-almost-a-year-after-initially-confirming-that-it-was-going-to-do-so.413904.0.html