Because right Shift + T, Caps Lock + t, and other left-Shift combinations work, and the problem also happens in Safe Mode and with the On-Screen Keyboard, this points away from Sticky Keys and a simple driver issue.
The most useful next checks are:
- Check the input language / keyboard layout
Go to Start > Settings > Time & language > Region & language and make sure the keyboard input language matches the language expected on the PC. A mismatched layout can cause some keys or key combinations to behave unexpectedly. - Check the Text Input Management Service
Since the issue affects input behavior, open Services by runningservices.msc.
Find Text Input Management Service.- Open Properties
- Make sure Startup type is Manual or Automatic, not Disabled
- If the service is stopped, start it
- Then sign out of Windows and sign back in
- Check for debris again and clean the key area
Even if debris is not obvious, inspect around the left Shift and T keys. Use compressed air to blow dust and debris from the surface and between the keys, or gently vacuum the top of the keyboard using a dusting brush. - Test with another keyboard if available
Connect another keyboard and test left Shift + T. If it works on the other keyboard, that strongly suggests the built-in keyboard hardware is the problem. - Use the On-Screen Keyboard as a temporary workaround
Windows includes the On-Screen Keyboard for typing without a physical keyboard while troubleshooting continues.
If the problem remains after those checks, the remaining evidence points most strongly to a hardware issue with the keyboard matrix or key circuitry, even if both keys still work separately in some cases.