No that won't work.

To compare Joint to MFS.  If you are using the Online version, do NOT change anything on your return.  You would have to start with a new account and do a test return.  You don't have to pay unless you want to print it out.  So you might need 3 accounts, one for Joint and two MFS, one for each spouse.

How to Compare Joint to Married Filing Separately

https://ttlc.intuit.com/community/married/help/how-can-we-compare-married-filing-jointly-with-marrie...

How to start another return in the Online version

https://ttlc.intuit.com/community/using-turbotax/help/how-do-i-start-another-return-in-turbotax-onli...

It would be better to use the Desktop CD/Download program.  It can do unlimited returns and has a What If worksheet to compare them and many other advantages over the online version.

You can buy the Desktop CD/Download program here

https://turbotax.intuit.com/personal-taxes/cd-download/ 

It is not easy to compare MFJ to MFS using online TT but you can do it.  Since you only get one return for each account and user ID, you have to use 3 accounts and user ID’s—one for MFJ and two for each of the MFS returns.  Compare, choose, and file—and pay—accordingly.

It is much easier to do this comparison using the desktop version of TT installed from a CD or downloaded to your own computer.  You pay once for the software and you can prepare multiple returns easily, and it has a “what if” feature that allows comparisons.

JOINT vs. SEPARATE RETURNS 2018 and beyond

If you were legally married at the end of 2020 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 $24,800 (+$1300 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...

Or use the WHAT IF tool:

- Click Forms Icon (upper right of screen) or Ctrl 2 (forms view)

- Click on the Open Form Icon

- In the “Type a form name.” area type What-If (with the dash), click on the name of the worksheet - click on Open Form

- You will see the worksheet on the right side of the screen; enter the information right into the form

- To get back to interview mode - click on the Step-by-Step Icon (upper right of screen) or Ctrl 1

Here's some info on filing Separate.

Unless you have a specific reason to file separate returns,

It is usually better to file Joint. Joint has the lowest tax rates and the highest Standard Deduction.   And if you are in a Community Property state MFS gets tricky to figure out.  Here's some things to consider about filing separately……

In the first place you each have to file a separate return, so that's two returns.  And if you are using the Online version that means using 2 accounts and paying the fees twice.  

Many people think they come out better when filing Married Filing Separate but they are probably doing it wrong.  If one person itemizes deductions then the other one must itemize too, even if it's less than the standard deduction, even if it is ZERO!  

And there are several credits you can't take when filing separately, like the

EITC Earned Income Tax Credit

Child Care Credit

Educational Deductions and Credits

And contributions to IRA and ROTH IRA are limited when you file MFS.

Also if you file Married Filing Separately up to 85`% of your Social Security becomes taxable right away even with zero other income.

See …….

https://ttlc.intuit.com/community/married/help/is-it-better-for-a-married-couple-to-file-jointly-or-...

2020 was an unusual year.  If one spouse became unemployed it is possible that Married Separate will make a BIG difference in the refund.  If the unemployed spouse received unemployment benefits, and their MAGI is under $150,000 there is a very good chance that filing Married Separate is beneficial (if MAGI is over $150,000 when filing jointly).   I do not use the online version of Turbo Tax.  Do a proforma version as Married Joint and then do each spouse as Married Separate to see the impact.  This could pay for your vacation!