Your refund likely dropped due to the calculation of the Spouse or common-law partner amount.
The Spouse or common-law partner amount is calculated both federally and provincially, and is calculated based on your spouse's net income.
The maximum Spouse or common-law partner amount for tax year 2020 is $12,298 or $13,229 (depending on your income), or $14,571 or $15,502 (depending on your income) if your spouse/partner is dependent on you because of a physical or mental impairment. The amount you qualify for decreases as your spouse's net income increases. When your spouse's net income is higher than the maximum, you are no longer eligible for this credit.
While filing your tax return, if you indicate that you are married but do not enter your spouse's income, TurboTax assumes that your spouse's income is zero, and applies the full credit to your return. But if the amount is incorrect, the CRA will likely locate the error and reassess both your and your spouse's returns. In this case, you would be liable for the balance outstanding, as well as penalty and interest.
Whether you file separately or together, your return will be more accurate if you include your spouse’s net income on your tax return. If you don’t know your spouse’s net income, the CRA recommends that you enter your best estimate.