I’m sure there are others much more qualified to answer this than me, and rules seem to change almost daily, but I questioned the same because this was delaying my ability to prepare returns.  

The IRS website stated the ERC has to go on the return for the same year the credit is calculated for, even if it means you have to amend the return.  So, credits for qtrs in 2020 would have to go on the 2020 return.  

I can’t tell you how disappointed I was to read this.