The IRS processing centers were closed for almost four months because of the Covid-19 pandemic. During that time they did not process any mailed tax returns. They didn't even open the mail that came in. They just recently started to reopen the processing centers and work through the backlog, but they have limited staff and the backlog is huge, so it's going to take a very long time. Your amended return is sitting in one of the large trailers of unopened mail that are parked outside the IRS processing center. They have literally millions of pieces of mail that they haven't opened yet.
Don't worry. They will get to your amended return, but it will be while. Do not send another copy or try to e-file it. Unfortunately there is nothing you can do but wait. You can check once a week or so at the link that xmasbaby0 gave you. Eventually it will show up.
