In answer to your question Will putting in either the original 1040 amount or the pending amended amount from the year 2020 form 7202 risk long delays or a rejection of my 2021 taxes and recovery rebate credit and full child tax credit?
In my opinion using the amended 2020 numbers is correct. If your 2020 amendment is not processed, could this risk long delays or rejection of your 2021 taxes, possibly. Your return would not be rejected but you may receive correspondence for the IRS with questions. If you received a letter you could simply respond by saying that you amended your 2020 that has not be processed yet.
Unless your return or the changes in the amended return would put you over the threshold for the recovery rebate credit. I
The child tax credit should hold up your child tax credit.
I cannot really give you advice on this matter. You probably will not like my recommendation, but I would hold off filing for a little bit yet. The more time you can give for your 2020 amendment to be processed the better off you would be.
