https://www.visajourney.com/timeline/aoslist.php?vtype=7&op8=All&interview=&xfr=&op1=d&op2=&op3=&op4=1&op5=5%2C6%2C8%2C9%2C10%2C11&cfl= will give you some idea.
While the most recent tax return is required, the concern is actually your annual income. If all you sent before was the 2020 tax return, that is not enough to verify this year's expected income and is probably why you got the RFE.
I would suggest responding to the RFE by completing a new I-864 listing your current annual income and provide your last few month's pay stubs. The most recent should show your current year-to-date income which by this time should be about $30,000 if you're expecting $40,000 for the year. Highlight the pay date and year-to-date income. I would also include an employment verification letter showing your pay rate, start date, and that the employment is expected to continue. This should be enough to verify that your income is sufficient.
