A T777 is a slip entered for Employment expenses that you might have claimed. It isn't usually carried forward. Have you gone over your 2021 and 2022 tax returns line by line to verify all the information? It may be a wrong entry in a wrong box. Verify all the slips in your CRA My Account to make sure you did enter all your slips properly, especially if you used auto-fill. Sometimes information is entered twice, once with auto-fill and further along by the person doing the return.
Don't hesitate to call CRA for details.