Why didn’t I receive my whole refund ?

TurboTax never knows about back taxes or child support you may owe.   But the IRS knows, and they will seize your refund if you owe such debts.   If the IRS reduced your refund, they will send you a letter explaining why.   Meanwhile----usually people who are delinquent in paying child support or who owe a significant amount of back taxes are already aware of it---were you surprised by the reduction of your refund?

 refund offset.

https://www.irs.gov/uac/tax-refund-offsets-pay-unpaid-debts

 IRS Treasury Offset Program Call Center at 1-800-304-3107

 https://www.irs.gov/uac/tax-refund-offsets-pay-unpaid-debts

https://ttlc.intuit.com/community/refunds/help/what-is-a-refund-offset/00/26301

Reduced Refund      https://www.irs.gov/taxtopics/tc203

 NOTE: You can contact the IRS Treasury Offset Program Call Center at 1-800-304-3107 to ask if they have an offset for you on file. TurboTax would not have that information.

https://turbotax.intuit.com/tax-tips/tax-payments/who-can-garnish-an-income-tax-refund/L7cPPzDyc