Can i do a final return for 2021 for my mom who passed away earlier this year. When i log in, it only lets me do 2020. and where do i enter the deceased date?

I am so sorry for your loss.   You'll want to start the return as if your mom was still alive. During the questionnaire, there will be a spot for you to check "This person passed away before filing the tax return". You'll want to check that option. Then file the rest of the return normally.