1. In late summer the IRS portal, Child Tax Credit Update Portal, will be updated to allow you to enter information about your child born in 2021 (Congratulations!).
2. No. You cannot add a child born in 2021 to your 2020 tax return. Only children born on or before 12/31/2020 can be claimed on the 2020 tax return.
3. Due to the public nature of this forum it is difficult to effectively help with tax return rejections. In general, if your return has been repeatedly rejected and you are making the corrections that have been requested, you may need to file a paper return. Before you do this though, I suggest you call a TurboTax agent. They will be able to verify your identity and look at your return and reject information to help you determine if it will be possible to e-file for 2020.