From Pub 501 2022 page 7, Filing Status, Married Filing Separately, Special Rules, 3:
3. You can't take the credit for child and dependent care expenses in most cases, and the amount you can exclude from income under an employer's dependent care assistance program is limited to $2,500 (instead of $5,000 on a joint return).
Emphasis mine.
From Instructions for Form 2441 (2022), Who Can Take the Credit or Exclude Dependent Care Benefits?, Married Persons Filing Separately:
If you don't meet all of the requirements to be treated as unmarried, you can’t generally take the credit. However, you can generally take the exclusion if you meet items 2 through 5.
Emphasis from website.
The income exclusion (Dependent Care FSA) is allowed for both those filing MFS at half the amount for MFJ filings.
It's the credit that is disallowed for both individuals filing MFS except for one of those who can be treated as unmarried.
Perhaps this changed from the 2021 reply above to the 2022 publication. I want to note it since this thread was a top result for me when I searched "dependent care fsa married filing separately".
