What changed from 2019 to 2020 that I have $406.00 due in Fed Taxes?

We cannot see your tax return---lots of things may have changed.

We cannot see your screen, your return or your account.  Have you entered ALL of your 2020 information?  All your income, etc.?  Many tax documents that you need do not arrive until late January or even February, so maybe you do not have it all there yet.

No one in this user forum can see your tax return or your screen.  There were major tax law changes that began with the 2018 tax year that seem to continue to surprise some people.  Personal exemptions of over $4000 per person were removed beginning with 2018 returns.

 Was something different for 2020?  Did you have less income due to the pandemic?  Did you receive unemployment compensation?  If so, did you have tax withheld from it?

There are a lot of variables that affect your refund or tax due including how much you earned, how much tax you had withheld, your filing status, the number of dependents you claim, your deductions and credits, etc.  You may have lost Earned Income Credit or the Child Tax Credit— did a child turn 17?  If you received the EIC last year, remember that changes in the amount you earn have a big effect on the amount of EIC you can get. (Sometimes earning more money means less EIC)  Are you 65 or older ?  If so, your standard deduction is higher. Everyone has a higher standard deduction now so it is harder to use itemized deductions.

And of course, always check your own data entries, looking for errors such as misplaced decimals or extra zeros.

https://ttlc.intuit.com/questions/1901008-why-did-my-refund-go-down-compared-to-last-year-s

Print out 2019 and 2020 and compare them side by side to see what is different.  The line numbers are different so it is tricky and you have to read them very carefully.