I've filed my return through mail for the year 2020, mailed it around 05/2020. When I check on IRS site, it says they have not received my return. Any advice?

@gajerasavan - hmmmm.... according the IRS website they have completed processing all paper filed tax returns received through December, 2021.... do you have any sort of confirmation that indeed the IRS received the return? did you trace the envelop when mailing? receiving anything from the IRS to date that they are working on it? looked at your transcript at IRS.GOV? 

This is why I stated above that my lean was to send it in again - unless you have evidence that they actually have it. 

this is what the IRS website states: 

How long you may have to wait: The IRS understands the importance of timely processing of tax returns and refund issuance. We have processed all error free returns received prior to December 2021 and continue to work the returns that need to be manually reviewed due to errors.  We are continuing to reroute tax returns and taxpayer correspondence from locations that are behind to locations where more staff is available, and we are taking other actions to minimize any delays. Tax returns are opened and processed in the order received. As the return is processed, whether it was filed electronically or on paper, it may be delayed because it has a mistake including errors concerning the Recovery Rebate Credit and the Child Tax Credit, is missing information, or there is suspected identity theft or fraud. If we can fix it without contacting you, we will. If we need more information or need you to verify that it was you who sent the tax return, we will write you a letter. The resolution of these issues could take 90 to 120 days depending on how quickly and accurately you respond, and the ability of IRS staff trained and working under social distancing requirements to complete the processing of your return.

https://www.irs.gov/newsroom/irs-operations-during-covid-19-mission-critical-functions-continue#collapseCollapsible1639064526818