Hi,
My husband and I are F1 students and qualified for 1040-NR.
To claim my husband's medical expense to my Flex account (I put too much money on this account), we need to file tax jointly.
However, I cannot find joint filing option in 1040-NR.
Can I use 1040 instead of 1040 NR?

On F1 both of you will file separate tax returns (if you are required) as nonresidents.
What is your country of citizenship?
Medical expenses is itemized deduction. Only expense more than 7.5% of your AGI is allowed.

Sorry, you CANNOT file a non-resident alien tax return jointly.