As per CRA- You may be able to claim the amount for an eligible dependant if, at any time in the year, you supported an eligible dependant and met certain conditions.
You cannot claim this amount if you claimed an amount for the year on line 30300 of your return. If you did not claim an amount on line 30300 of your return, you may be able to claim this amount for one dependant if, at any time in the year, you met all the following conditions:
You did not have a spouse or common-law partner or, if you did, you were not living with them, supporting them, or being supported by them
You supported the dependant in 2021
You lived with the dependant (in most cases in Canada) in a home you maintained. You cannot claim this amount for a person who was only visiting.
Only the parent who does not pay child support can claim the amount for an eligible dependant on line 30400 of their tax return