Yes you can file your 2020 tax return even though your amended 2019 return has not been confirmed as accepted.
Be sure that if there were any carryovers or other information that was on the amended return, that it carried over onto the 2020.
The staffing of the IRS is likely going to cause a lot of delays for early tax filers. The reason is simple: with many IRS workers stuck at home or sick due to the pandemic, there will be delays.
Combine that with the additional stimulus checks (which require staffing and programming to send out), and the last minute tax changes that passed in December (which also require programming and testing), the IRS is stretched to the limits.
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as to 2019, the IRS may have a multimillion backlog for that year.
you can try calling
First choose your language.
When asked for SSN do nothing it will ask twice
You should then be transferred to an agent, but there is likely to be a long wait.