So, my husband and I normally file Married file jointly but I have found that if we file separately this year we get a better tax break. Can you file separate for just one year.?

Yes, you can. Be careful if you are itemizing deductions. You can't both take the same deduction, you must divide it. You can do this in any way that works for you. In addition, one of you can't itemize and have the other take the standard deduction.

By filing separate it looks as though I am able to receive the 3rd stimulus payment.  Am I able to collect this even though our combined income was above the limit?

Yes, if you meet all the qualifications and your individual income is below the limit then you can claim the Recovery Rebate Credit for the missing third stimulus on your tax return.

To claim the Recovery Rebate Credit in TurboTax, please follow these steps:

1. After entering all your information click "Search" at the top right and type "Stimulus".
2.  Follow the jump to link (if you do not qualify for the Recovery Rebate Credit the stimulus questions will not come up). 
3. On the screen "Let's double-check the amount you received" you will be asked about the amount of third stimulus payment you received. TurboTax will then calculate the amount of stimulus payment remaining that you are still entitled to get. 
4. Any stimulus amount remaining due to you will show as The Recovery Rebate Credit on line 30 of Form 1040.

To be eligible for the Recovery Rebate Credit you need to be a U.S. citizen or U.S. resident alien in 2021 and have a Social Security number that is valid for employment.

You cannot be claimed as a dependent by someone else to be eligible. 

Your credit amount will be reduced if your 2021 adjusted gross income (AGI) is more than: 

• $150,000 if married and filing a joint return or filing as a qualifying widow or widower
• $112,500 if filing as head of household or
• $75,000 for eligible individuals filing as a single or as married filing separately.  

Your payment will be reduced by 5% of the amount by which your AGI exceeds the applicable threshold above. (IRS FAQ Recovery Rebate Credit )

Please see What are the eligibility rules for the Recovery Rebate Credit? for additional information.

Be careful with splitting income and deductions if you live in a community property state and file MFS.  Community property states are Louisiana, Arizona, California, Texas, Washington, Idaho, Nevada, New Mexico, and Wisconsin.