Why does the standard deduction section box checked for someone can claim spouse as dependent when we filed separately and i didn't choose that box?

[KrisD15]

When you file separately from your spouse, you must both use the same method, either Itemized Deductions OR use the Standard Deduction. 

Since you indicated that your spouse could be claimed as a dependent, you have indicated that your spouse will/can only use the standard deduction. Dependents cannot itemize. 

Whether your spouse files a tax return is immaterial. Because he or she is a dependent, you must both use the Standard Deduction. 

IRS Topic 551

[Lauraaott]

This happened to me as well. I didn’t check the box, but when I didn’t get my third stimulus check I reviewed my 2020 taxes. Is this the reason I did not get third stimulus? I know I’m eligible....I’m a teacher and make way less than $75,000. 
I read this box (someone can claim: your spouse as a dependent) can cause you to not receive 3rd check. 
Do I need to amend on March 25? If so, when will I get 3rd check? 
Thanks so much! 

[KrisD15]

No, 

this would not stop you from being eligible for the stimulus payments however your spouse would not be eligible for the first two. 

It means you cannot Itemize Deductions. You must take the Standard Deduction which most people do regardless. 

[Lauraaott]

Well then what would make me not eligible or what information could the IRS be missing? 
I make less than $50,000 and have a dependent. We are married but file MFS.

Thanks!

[Irene2805]

Just because you haven't received the third stimulus payment yet doesn't mean you won't.  For information on when you can expect your stimulus payment, check the IRS Get My Payment tool.   For more information please see this TurboTax Help article:  How will the third stimulus impact me?

@Lauraaott