Can I claim my stepson as a dependent even though my wife made more money & were filing separately?

[xmasbaby0]

  If you are legally married to the child's mother, a step-child can be claimed on your return.  But..........Why are you filing separate returns?  That is usually the worst way to file.

If you were legally married at the end of 2022 your filing choices are married filing jointly or married filing separately.

Married Filing Jointly is usually better, even if one spouse had little or no income. When you file a joint return, you and your spouse will get the married filing jointly standard deduction of $25,900 (+$1400 for each spouse 65 or older)  You are eligible for more credits including education credits, earned income credit, child and dependent care credit, and a larger income limit to receive the child tax credit. 

If you choose to file married filing separately, both spouses have to file the same way—either you both itemize or you both use standard deduction. Your tax rate will be higher than on a joint return. Some of the special rules for filing separately include: you cannot get earned income credit, education credits, adoption credits, or deductions for student loan interest. A higher percent of your Social Security benefits may be taxable. Your limit for SALT (state and local taxes and sales tax) will be only $5000 per spouse. In many cases you will not be able to take the child and dependent care credit. The amount you can contribute to a retirement account will be affected. If you live in a community property state, you will be required to provide additional information regarding your spouse’s income. ( Community property states:  AZ, CA, ID, LA, NV, NM, TX, WA, WI)

 If  you are using online TurboTax to prepare your returns, you will need to prepare two separate returns and pay twice.

https://ttlc.intuit.com/questions/1894449-married-filing-jointly-vs-married-filing-separately

https://ttlc.intuit.com/questions/1901162-married-filing-separately-in-community-property-states

https://ttlc.intuit.com/questions/1894449-is-it-better-for-a-married-couple-to-file-jointly-or-separ...

[Opus 17]

If you live together, either one of you may claim the child, but not both. A stepparent has the same legal rights to claim a child as a dependent as a biological child, and this right continues even if you divorce the other parent.  

if you can’t agree and both claim the child, the IRS will apply the tiebreaker rules and award the dependent to the parent with the higher income. But if you both agree that you should claim the child, that’s fine, even though your income is lower.

If you are living apart, then generally speaking, only the parent where the child lives more than half the year can claim a child as a dependent.