Windows speech input (Win + H) only works if the cursor is inside an editable text field, if you always see the message “Speech input only works in text fields” even in Word or Notepad, it usually means:
Windows is not detecting the input field correctly, or
The speech language does not match the keyboard input language.
If you use multiple accounts and it works in one but not the other, compare:
Input methods / keyboards installed
Speech language settings
Privacy & microphone permissions (Settings > Privacy & Security > Microphone > allow apps to access microphone).