Hey moreba23,
There is an article we can share that has a few suggestions you can look at and see if you can get the Shift key to respond.
The below information is found in the article, If your Mac doesn't respond to key presses- Apple Support.
If other keys don’t work
You may have accidentally set an option that changes how your keyboard operates.
• Choose Apple menu
> System Settings, click Accessibility
in the sidebar, then click Keyboard on the right. (You may need to scroll down.) Make sure Slow Keys is turned off. If Slow Keys is on, you must press and hold a key longer than usual before it’s recognized.
• Choose Apple menu > System Settings, click Accessibility in the sidebar, then click Pointer Control on the right. (You may need to scroll down.) Make sure Mouse Keys is off.
• Choose Apple menu > System Settings, then click Keyboard
in the sidebar. (You may need to scroll down.) Click Edit next to Input Sources on the right, then turn on “Show Input menu in menu bar.” Open the Input menu, then make sure the correct keyboard layout is selected.
If you are still unable to get the Shift key to respond, you will want to reach out to Apple Support for further help.
Good luck!