If your husband agrees you can still file a joint return. You are not "supporting" him in jail and cannot claim him as a dependent if that is what you were hoping. You might be providing him with some money or small items but he is supported by other taxpayers' money in the facility he is in.
Or....if you have been apart for at least the last six months of the tax year and you have dependent children you could file as Head of Household.
The advantages of joint return:
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.
If you file HOH then you claim the kids as your dependents and your standard deduction is $18,650. Nothing about your spouse goes on your return if you file HOH.
Assuming that your husband has little or no income, your best financial situation will be to file a joint return. You can do this even though he is incarcerated and even if he has no income. You only have to agree to file jointly.
if you don’t agree to file jointly or you want to file separately for some other reason, then you could file as head of household if you provide care in your home for a qualifying dependent.