Plugin IdeaVim: U Key not Working

With IdeaVim plugin enabled, the capitalized U is not working as expected. (The lowercased u, and others like `hjkl` and etc, is working properly)

Is it not implemented yet? 

If yes, may I ask where to find the docs about which functionality is not currently implemented yet?

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The verison that I am using:

IntelliJ IDEA 2023.1.5 (Ultimate Edition)
Build #IU-231.9392.1, built on July 25, 2023
Runtime version: 17.0.7+10-b829.16 amd64
VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o.
Windows 10.0
GC: G1 Young Generation, G1 Old Generation
Memory: 2002M
Cores: 12
Registry:
   debugger.watches.in.variables=false
   debugger.new.tool.window.layout=true
   ide.experimental.ui=true

Non-Bundled Plugins:
   leetcode-editor (8.8)
   com.vecheslav.darculaDarkerTheme (1.2.0)
   org.jetbrains.plugins.go (231.9392.1)
   AceJump (3.8.16)
   IdeaVIM (2.6.3)
   com.github.copilot (1.3.3.3572)
   org.jetbrains.IdeaVim-EasyMotion (1.10)
   com.samdark.intellij-visual-studio-code-dark-plus (2.8)
   com.intellij.kubernetes (231.9011.4)
   com.github.dinbtechit.vscodetheme (1.10.6)

Kotlin: 231-1.9.10-release-459-IJ8770.65