The normal processing time for an amended return is about 4 months, but this year is not normal. The IRS is severely backlogged. You should expect it to take 6 months or more for your amended return to be processed. From your other posts it sounds like you filed the amended return before your original return was processed. That might cause further delays, regardless of the reason that your original return has not been processed.
If you do not get the third stimulus payment during the year, you will be able to claim it as a Recovery Rebate Credit on your 2021 tax return.
