This is probably a configuration issue with the Operating System. If you have accessibility options enabled, it can interfere with the normal system shortcuts. So, start by checking the accessibility options in your keyboard preferences.
If all is well there, the other common issue is language/keyboard mismatch. For example, if you have a system set up in in US English, but you have a Spanish Keyboard, you have to ensure that the correct keyboard is selected in order to have the correct key mapping. For example, the images below (For US and Spainish Keyboards) show that the “+” key is in two different places. So if I set my keyboard to be US English when I have a Spanish Keyboard, then the shortcuts won’t work as expected.
So, Check your keyboard settings to make sure it reflects the actual keyboard you are using. Remember, even if you have a US keyboard, there can be differences depending on the keyboard you have. Some are Magic Keyboards as shown above, others are extended keyboards or international keyboards / it all depends what your keyboard layout is:
The easiest way to check if this could be the issue, just open the keyboard viewer (as illustrated above) and check that the keys displayed in the viewer are the same as the keys on your keyboard.