If you decide to file your tax return as Married Filing Jointly you must apply for an ITIN with the tax return and you would need to be providing a statement with your tax return that you want your Nonresident Alien Spouse Treated as a Resident. See IRS Publication 54 Tax Guide for U.S. Citizens and Resident Aliens Abroad pages 6 and 7 - https://www.irs.gov/pub/irs-pdf/p54.pdf
Yes, since your were married at the end of 2020 you can file as Married filing joint. You can apply for a ITIN with your tax return. The following has information on getting a ITIN.
