See this TurboTax support FAQ for possible explanations - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-refund/refund-drop-entered-second-w-2/L4wmMMBCs_US_en_US?uid=lsqnfffy
More income = more tax
That was normal.
WHY DID MY REFUND GO DOWN WHEN I ADDED ANOTHER W-2?
You started off with your first W-2 and your refund looked high? Then you added another W-2 and it stopped looking so good? That is normal. When you added more income, your tax liability increased, so you saw your refund decrease. The program began by giving you your standard deduction—- which lowered your taxable income. (if you are filing joint it took $27,700 off your income right off the bat) So you are not being taxed on as much of the income on that first W-2. Then you added taxable income--so the refund went down. Your refund (or tax due) is based on the total of your income, not “per W-2.”
And…adding income may affect other credits you were getting like the earned income credit.
Wait until you have entered ALL of your income and credit/deduction information. You can't really tell anything until it is all entered. That “refund monitor” does not mean anything until everything has been entered.
https://ttlc.intuit.com/questions/2273878-why-did-my-refund-drop-when-i-entered-another-w-2