I had to submit my 2019 taxes manually due to special tax situation. I went to irs.gov to search my but I do not have any refund amount - how do know if IRS received it?

Why aren't you putting in your actual refund amount?  Or did you have a tax due?

Sorry the IRS has limited staff due to Covid-19.  They didn't start opening the mail until June that's been stacking up. Back in March the IRS closed their processing centers and stopped processing mailed tax returns.  An IRS spokesperson recently said that they have about 11 million pieces of unopened mail.  The IRS says....."We’re experiencing delays in processing paper tax returns due to limited staffing. If you already filed a paper return, we will process it in the order we received it."  So it may take longer if you mailed in June or later.  So you have to keep waiting.

See this IRS page for the latest information

https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue

If you do not have a federal tax refund the IRS website for a refund status would not be of any use.

If you mailed your tax return and did not use a tracking service from the US Post Office you will not have any verification that the IRS received your tax return.

The IRS was not processing any paper tax returns for several months due to the pandemic and limited staffing.  They have only just recently started to process approximately 11 million paper return in the order they were received.

Go to this IRS website for information - https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue

We’re experiencing delays in processing paper tax returns due to limited staffing. If you already filed a paper return, we will process it in the order we received it.

Do not file a second tax return or contact the IRS about the status of your return.