Hey George, sorry to hear you're stuck with this annoying issue—those underlined letter shortcuts are total time-savers, so I get why this is frustrating. Let's go through some practical fixes that usually get things working again on Windows 10 with Word 2019:

• 检查Word的屏幕提示快捷键设置
  Open Word, head to File > Options > Customize Ribbon. Look for the "Keyboard shortcuts: Customize" button at the bottom right of the window. In the pop-up, make sure the "Show shortcut keys in ScreenTips" option is checked. Sometimes this setting gets toggled off by accident, which hides the underlined letters and disables the shortcut functionality entirely.

• 关闭筛选键功能
  Windows' Filter Keys accessibility feature can sometimes block or interfere with keyboard shortcuts. Here's how to check:

  1. Press Win + I to open Settings, then go to Ease of Access > Keyboard.
  2. Find the "Filter keys" option and make sure it's turned off. If it was enabled, disable it and restart Word to test the shortcuts.

• 修复Office安装文件
  Corrupted Office files often cause weird glitches like this. Try repairing your installation:

  1. Open Settings > Apps > Apps & features.
  2. Locate Microsoft Office 2019 in the list, click it, then select "Modify".
  3. Start with "Quick Repair" (it's faster and usually fixes minor issues) — if that doesn't work, go for "Online Repair" which does a more thorough fix. Follow the prompts, restart your computer, and check Word again.

• 更新Word和Windows系统
  Outdated software can have bugs that break features. Make sure both are up to date:

  • For Word: Go to File > Account > Update Options > Update Now to install any pending Office updates.
  • For Windows: Open Settings > Update & Security > Windows Update > Check for updates to get the latest system patches.

• 在安全模式下测试Word
  Third-party add-ins can sometimes interfere with Word's normal functions. To open Word in Safe Mode:
  Press Win + R, type winword /safe, and hit Enter. If the shortcuts work here, you'll need to track down the problematic add-in:

  1. Go to File > Options > Add-ins.
  2. Select "COM Add-ins" from the dropdown at the bottom, click "Go".
  3. Uncheck one add-in at a time, restart Word, and test the shortcuts until you find the one causing the issue.

Give these steps a shot one by one—I'm confident one of them will resolve the problem. Let me know if you hit any snags along the way!

备注：内容来源于stack exchange，提问作者George Lee