You say that you "just" got custody of a child---so we do not know if you will even be able to claim that child as a dependent on your 2020 return. Who did the child live with for the time before you got physical custody? Did the child live with you--or someone else? The person who the child lived with for more than 183 nights in 2020 is the one who will be able to claim the child as a dependent for 2020.
IRS interview to help determine who can be claimed:
https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent
https://ttlc.intuit.com/questions/3113432-who-can-i-claim-as-my-dependent
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
