My father passed away in Jan 2021, after year end

Your father's taxes would be filed as usual, including using his social security number.  Include income only up to the date of death that he actually received before death. When filing you will answer the question about whether he is deceased and enter the date of death.  'I'm preparing this return for ______, who has passed away'

 

Any question that asks about the whole year, you would consider only the time he was alive (as though it was a whole year).

 

If there is a refund, then Form 1310 will also be included with the tax return.

• Open the TurboTax account > Use Search (upper right) > Type form 1310 > Press enter > Jump to .... link
• Continue to complete the form as requested - Your answers are important to complete the tax return (see the image below)

don't include income he received in 2021, although that's probably zero (so far).

Sorry for your loss.

 you need an Estate bank account with an EIN from the IRS to handle the affairs properly.