In normal times it takes up to 16 weeks or more to process an Amended 1040X return. But these are not normal times. They just started opening the mail in 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 you have to keep waiting.
See this IRS page for the latest information